Method of processing a wafer

ABSTRACT

The invention relates to methods of processing a wafer, having on one side a device area with a plurality of devices. In particular, the invention relates to a method which comprises providing a protective film, and applying the protective film to the side of the wafer being opposite to the one side, so that at least a central area of a front surface of the protective film is in direct contact with the side of the wafer being opposite to the one side. The method further comprises applying an external stimulus to the protective film during and/or after applying the protective film to the side of the wafer being opposite to the one side, so that the protective film is attached to the side of the wafer being opposite to the one side, and processing the one side of the wafer and/or the side of the wafer being opposite to the one side.

This is a divisional application of application Ser. No. 16/247,895filed Jan. 15, 2019, which claims the benefit of German PatentApplication No. 10 2018 200 656.3, filed on Jan. 16, 2018.

TECHNICAL FIELD

The present invention relates to methods of processing a wafer, such asa semiconductor wafer, having on one side a device area with a pluralityof devices.

TECHNICAL BACKGROUND

In a semiconductor device fabrication process, a wafer having a devicearea with a plurality of devices, commonly partitioned by a plurality ofdivision lines, is divided into individual dies. This fabricationprocess generally comprises a grinding step for adjusting the waferthickness and a cutting step of cutting the wafer along the divisionlines to obtain the individual dies. The grinding step is performed froma back side of the wafer which is opposite to a wafer front side onwhich the device area is formed. Moreover, also other processing steps,such as polishing and/or etching, may be carried out on the back side ofthe wafer. The wafer may be cut along the division lines from its frontside or its back side.

In order to protect the devices formed on the wafer, e.g., frombreakage, deformation and/or contamination by debris, grinding water orcutting water, during processing of the wafer, a protective film orsheeting may be applied to the front side of the wafer prior toprocessing.

Such protection of the devices is particularly important if the devicearea has an uneven surface structure. For example, in knownsemiconductor device fabrication processes, such as Wafer Level ChipScale Package (WLCSP), the device area of the wafer is formed with aplurality of protrusions, such as bumps, protruding from a plane surfaceof the wafer. These protrusions are used, for example, for establishingan electrical contact with the devices in the individual dies, e.g.,when incorporating the dies in electronic equipment, such as mobilephones and personal computers.

In order to achieve a size reduction of such electronic equipment, thesemiconductor devices have to be reduced in size. Hence, wafers havingthe devices formed thereon are ground in the grinding step referred toabove to thicknesses in the μm range, e.g., in the range from 20 to 100μm.

In known semiconductor device fabrication processes, problems may ariseduring processing, e.g., in the grinding step, if protrusions, such asbumps, are present in the device area. In particular, due to thepresence of these protrusions, the risk of breakage of the wafer duringprocessing is significantly increased. Further, if the wafer is groundto a small thickness, e.g., a thickness in the μm range, the protrusionsof the device area on the front side of the wafer may cause adeformation of the wafer back side, thus compromising the quality of theresulting dies.

Therefore, the use of a protective film or sheeting is of particularimportance when processing wafers with device areas having such unevensurface structures.

However, in particular, for the case of sensitive devices, such as MEMS,there is a problem in that the device structure on the wafer may bedamaged by the adhesive force of an adhesive layer formed on theprotective film or sheeting or may be contaminated by adhesive residueson the devices, when the film or sheeting is peeled off from the wafer.

A protective film or sheeting may be applied to the back side of thewafer prior to processing, in order to protect the wafer, e.g., frombreakage, deformation and/or contamination by debris, for example,during a step of cutting the wafer.

Also in this case, there is a problem that the wafer may be damaged bythe adhesive force of an adhesive layer formed on the protective film orsheeting or may be contaminated by adhesive residues on the wafer, whenthe film or sheeting is peeled off from the wafer.

Hence, there remains a need for a reliable and efficient method ofprocessing a wafer having a device area which allows for any risk ofcontamination and damage to the wafer to be minimised.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide areliable and efficient method of processing a wafer having a device areawhich allows for any risk of contamination and damage to the wafer to beminimised. This goal is achieved by a wafer processing method with thetechnical features of claim 1, by a wafer processing method with thetechnical features of claim 9 and by a wafer processing method with thetechnical features of claim 19. Preferred embodiments of the inventionfollow from the dependent claims.

The invention provides a method of processing a wafer having on one sidea device area with a plurality of devices. The method comprisesproviding a protective film or sheet and applying the protective film orsheet to the side of the wafer being opposite to the one side, so thatat least a central area of a front surface of the protective film orsheet is in direct contact with the side of the wafer being opposite tothe one side. Further, the method comprises applying an externalstimulus to the protective film or sheet during and/or after applyingthe protective film or sheet to the side of the wafer being opposite tothe one side, so that the protective film or sheet is attached to theside of the wafer being opposite to the one side, and processing the oneside of the wafer and/or the side of the wafer being opposite to the oneside.

The protective film is applied to the side of the wafer being oppositeto the one side, i.e., to the wafer back side, so that at least thecentral area of the front surface of the protective film is in directcontact with the side of the wafer being opposite to the one side. Thus,no material, in particular, no adhesive, is present between at least thecentral area of the front surface of the protective film and the side ofthe wafer being opposite to the one side.

Therefore, the risk of a possible contamination of or damage to thewafer, e.g., due to an adhesive force of an adhesive layer or adhesiveresidues on the wafer, can be significantly reduced or even eliminated.

During and/or after applying the protective film to the side of thewafer being opposite to the one side, the external stimulus is appliedto the protective film, so that the protective film is attached to theside of the wafer being opposite to the one side. An attachment forcebetween protective film and wafer, holding the protective film in itsposition on the wafer, is thus generated through the application of theexternal stimulus. Hence, no additional adhesive material is necessaryfor attaching the protective film to the side of the wafer beingopposite to the one side.

In particular, by applying the external stimulus to the protective film,a form fit, such as a positive fit, and/or a material bond, such as anadhesive bond, may be formed between the protective film and the wafer.The terms “material bond” and “adhesive bond” define an attachment orconnection between protective film and wafer due to atomic and/ormolecular forces acting between these two components.

The term “adhesive bond” relates to the presence of these atomic and/ormolecular forces, which act so as to attach or adhere the protectivefilm to the wafer, and does not imply the presence of an additionaladhesive between protective film and wafer. Rather, at least the centralarea of the front surface of the protective film is in direct contactwith the side of the wafer being opposite to the one side, as has beendetailed above.

The method of the present invention thus enables reliable and efficientprocessing of a wafer having a device area, minimising any risk ofcontamination and damage to the wafer.

The wafer back side surface may be a substantially flat, even surface ora flat, even surface. Alternatively, protrusions or projectionsprotruding from a plane wafer surface along the thickness direction ofthe wafer may be present on the back side of the wafer.

Applying the external stimulus to the protective film may comprise orconsist of heating the protective film and/or cooling the protectivefilm and/or applying a vacuum to the protective film and/or irradiatingthe protective film with radiation, such as light, e.g., by using alaser beam.

The external stimulus may comprise or be a chemical compound and/orelectron or plasma irradiation and/or mechanical treatment, such aspressure, friction or ultrasound application, and/or static electricity.

Particularly preferably, applying the external stimulus to theprotective film comprises or consists of heating the protective film.For example, applying the external stimulus to the protective film maycomprise or consist of heating the protective film and applying a vacuumto the protective film. In this case, the vacuum may be applied to theprotective film during and/or before and/or after heating the protectivefilm.

If applying the external stimulus to the protective film comprises orconsists of heating the protective film, the method may further compriseallowing the protective film to cool down after the heating process. Inparticular, the protective film may be allowed to cool down to itsinitial temperature, i.e., to the temperature thereof prior to theheating process. The protective film may be allowed to cool down, e.g.,to its initial temperature, before processing the one side of the wafer,i.e., the wafer front side, and/or the side of the wafer being oppositeto the one side, i.e., the wafer back side.

An attachment force between protective film and wafer is generatedthrough the heating process. The attachment of the protective film tothe wafer may be caused in the heating process itself and/or in asubsequent process of allowing the protective film to cool down.

The protective film may be softened by the heating process, e.g., so asto conform to the wafer surface on the side of the wafer being oppositeto the one side, for example, absorbing the wafer topography. Uponcooling down, e.g., to its initial temperature, the protective film mayreharden, e.g., so as to create a form fit and/or a material bond to thewafer.

The protective film may be heat resistant up to a temperature of 180° C.or more, preferably up to a temperature of 220° C. or more, morepreferably up to a temperature of 250° C. or more, and even morepreferably up to a temperature of 300° C. or more.

The protective film may be heated to a temperature in the range of 30°C. to 250° C., preferably 50° C. to 200° C., more preferably 60° C. to150° C. and even more preferably 70° C. to 110° C. Particularlypreferably, the protective film is heated to a temperature ofapproximately 80° C.

The protective film may be heated over a duration in the range of 30 secto 10 min, preferably 1 min to 8 min, more preferably 1 min to 6 min,even more preferably 1 min to 4 min and yet more preferably 1 min to 3min, during and/or after applying the protective film to the side of thewafer being opposite to the one side.

If applying the external stimulus to the protective film comprises orconsists of heating the protective film, the protective film may bedirectly and/or indirectly heated.

The protective film may be heated by directly applying heat thereto,e.g., using a heat application means, such as a heated roller, a heatedstamp or the like, or a heat radiation means. The protective film andthe wafer may be placed in a receptacle or chamber, such as a vacuumchamber, and an inner volume of the receptacle or chamber may be heated,so as to heat the protective film. The receptacle or chamber may beprovided with a heat radiation means.

The protective film may be indirectly heated, e.g., by heating the waferbefore and/or during and/or after applying the protective film to theside of the wafer being opposite to the one side. For example, the wafermay be heated by placing the wafer on a support or carrier, such as achuck table, and heating the support or carrier.

For example, the support or carrier, such as a chuck table, may beheated to a temperature in the range of 30° C. to 250° C., preferably50° C. to 200° C., more preferably 60° C. to 150° C. and even morepreferably 70° C. to 110° C. Particularly preferably, the support orcarrier may be heated to a temperature of approximately 80° C.

These approaches may also be combined, for example, by using a heatapplication means, such as a heated roller or the like, or a heatradiation means for directly heating the protective film, and alsoindirectly heating the protective film through the wafer.

If applying the external stimulus to the protective film comprises orconsists of heating the protective film, it is preferable that theprotective film is pliable, elastic, flexible, stretchable, soft and/orcompressible when in its heated state. In this way, it can beparticularly reliably ensured that the protective film conforms to thewafer surface on the side of the wafer being opposite to the one side,for example, absorbing the wafer topography. This is especiallyadvantageous if protrusions, such as surface unevenness or roughness,bumps, optical elements or the like, protruding along a thicknessdirection of the wafer are present on the wafer back side, as will befurther detailed below.

Preferably, the protective film, at least to some degree, hardens orstiffens upon cooling down, so as to become more rigid and/or robust inthe cooled down state. In this way, particularly reliable protection ofthe wafer during subsequent processing of the wafer, such as cutting thewafer, can be ensured.

The method may further comprise, during and/or after applying theprotective film to the side of the wafer being opposite to the one side,applying pressure to a back surface of the protective film opposite tothe front surface thereof. In this way, the front surface of theprotective film is pressed against the side of the wafer being oppositeto the one side. Thus, it can be particularly efficiently ensured thatthe protective film is reliably attached to the wafer.

If applying the external stimulus to the protective film comprisesheating the protective film, the pressure may be applied to the backsurface of the protective film before and/or during and/or after heatingthe protective film. The pressure may be applied to the back surface ofthe protective film before processing the front side and/or the backside of the wafer.

The pressure may be applied to the back surface of the protective filmby a pressure application means, such as a roller, a stamp, a membraneor the like.

Particularly preferably, a combined heat and pressure application means,such as a heated roller or a heated stamp, may be used. In this case,pressure can be applied to the back surface of the protective filmwhile, at the same time, heating the protective film.

The pressure may be applied to the back surface of the protective filmin a vacuum chamber, as will be further detailed below.

The protective film may be applied and/or attached to the back side ofthe wafer in a reduced pressure atmosphere, in particular, under avacuum. In this way, it can be reliably ensured that no voids and/or airbubbles are present between the protective film and the wafer. Hence,any stress or strain on the wafer during processing the front sideand/or the back side thereof, e.g., due to such air bubbles expanding inthe heating process, is avoided.

For example, the step or steps of applying and/or attaching theprotective film to the side of the wafer being opposite to the one sidemay be carried out in a vacuum chamber. In particular, the protectivefilm may be applied and/or attached to the side of the wafer beingopposite to the one side by using a vacuum laminator. In such a vacuumlaminator, the wafer is placed on a chuck table in a vacuum chamber in astate in which the wafer front side is in contact with an upper surfaceof the chuck table and the wafer back side is oriented upward. The chucktable may be, for example, a heated chuck table.

The protective film to be applied to the wafer back side is held at itsperipheral portion by an annular frame and placed above the wafer backside in the vacuum chamber. An upper part of the vacuum chamber which issituated above the chuck table and the annular frame is provided with anair inlet port closed by an expandable rubber membrane.

After the wafer and the protective film have been loaded into the vacuumchamber, the chamber is evacuated and air is supplied through the airinlet port to the rubber membrane, causing the rubber membrane to expandinto the evacuated chamber. In this way, the rubber membrane is moveddownward in the vacuum chamber so as to push the protective film againstthe wafer back side, sealing the peripheral wafer portion with theprotective film and pressing the film against the wafer back side.Hence, the protective film can be applied closely to the wafer backside, e.g., so as to follow the contours of protrusions or projections,if such protrusions or projections are present.

The protective film may be heated during and/or after applicationthereof to the side of the wafer being opposite to the one side, e.g.,by heating the chuck table.

Subsequently, the vacuum in the vacuum chamber is released and theprotective film is held in its position on the wafer back side by theattachment force generated through the heating process and the positivepressure in the vacuum chamber.

Alternatively, the rubber membrane can be replaced by a soft stamp or asoft roller, e.g., a heated soft stamp or a heated soft roller.

The method may further comprise removing the protective film from thewafer after processing the front side and/or the back side thereof.Before and/or during removal of the protective film from the wafer, anexternal stimulus, such as heat, may be applied to the protective film.In this way, the removal process can be facilitated.

The wafer may further have, on the front side thereof, a peripheralmarginal area having no devices and being formed around the device area.

The wafer may be, for example, a semiconductor wafer, a glass wafer, asapphire wafer, a ceramic wafer, such as an alumina (Al₂O₃) ceramicwafer, a quartz wafer, a zirconia wafer, a PZT (lead zirconate titanate)wafer, a polycarbonate wafer, a metal (e.g., copper, iron, stainlesssteel, aluminium or the like) or metalised material wafer, a ferritewafer, an optical crystal material wafer, a resin, e.g., epoxy resin,coated or molded wafer or the like.

In particular, the wafer may be, for example, a Si wafer, a GaAs wafer,a GaN wafer, a GaP wafer, an InAs wafer, an InP wafer, a SiC wafer, aSiN wafer, a LT (lithium tantalate) wafer, a LN (lithium niobate) waferor the like.

The wafer may be made of a single material or of a combination ofdifferent materials, e.g., two or more of the above-identifiedmaterials. For example, the wafer may be a Si and glass bonded wafer, inwhich a wafer element made of Si is bonded to a wafer element made ofglass.

The wafer may have any type of shape. In a top view thereon, the wafermay have, for example, a circular shape, an oval shape, an ellipticalshape or a polygonal shape, such as a rectangular shape or a squareshape.

The protective film may have any type of shape. In a top view thereon,the protective film or sheet may have, for example, a circular shape, anoval shape, an elliptical shape or a polygonal shape, such as arectangular shape or a square shape.

The protective film may have substantially the same shape or the sameshape as the wafer.

The protective film may have an outer diameter which is larger than anouter diameter of the wafer. In this way, processing, handling and/ortransport of the wafer can be facilitated. In particular, an outerperipheral portion of the protective film can be attached to an annularframe, as will be detailed below.

The protective film may have an outer diameter which is smaller than theouter diameter of the wafer.

The protective film may have an outer diameter which is substantiallythe same as the outer diameter of the wafer.

The method may further comprise cutting the protective film. Theprotective film may be cut so that it has an outer diameter which islarger than the outer diameter of the wafer or smaller than the outerdiameter of the wafer or substantially the same as the outer diameter ofthe wafer.

The step of cutting the protective film may be performed before or afterapplying the protective film to the wafer.

The step of cutting the protective film may be performed before or afterattaching the protective film to the wafer.

The method may further comprise attaching an outer peripheral portion ofthe protective film to an annular frame. In particular, the outerperipheral portion of the protective film may be attached to the annularframe so that the protective film closes a central opening of theannular frame, i.e., the area inside the inner diameter of the annularframe. In this way, the wafer, which is attached to the protective film,in particular, to a central portion thereof, is held by the annularframe through the protective film. Thus, a wafer unit, comprising thewafer, the protective film and the annular frame, is formed,facilitating processing, handling and/or transport of the wafer.

The step of attaching the outer peripheral portion of the protectivefilm to the annular frame may be performed before or after applying theprotective film to the wafer.

The step of attaching the outer peripheral portion of the protectivefilm to the annular frame may be performed before or after attaching theprotective film to the wafer.

The step of attaching the outer peripheral portion of the protectivefilm to the annular frame may be performed before or after processingthe front side and/or the back side of the wafer.

At least one division line may be formed on the one side of the wafer. Aplurality of division lines may be formed on the one side of the wafer.The one or more division lines partition the devices formed in thedevice area.

The width of the at least one division line may be in the range of 30 μmto 200 μm, preferably 30 μm to 150 μm and more preferably 30 μm to 100μm.

The method may comprise processing the one side of the wafer, i.e., thewafer front side. Processing the one side of the wafer may comprise orconsist of removing wafer material along the at least one division line.If a plurality of division lines is formed on the one side of the wafer,processing the one side of the wafer may comprise or consist of removingwafer material along each of the plurality of division lines.

The wafer material may be removed along the at least one division linethroughout the entire thickness of the wafer. In this case, the wafer isdivided along the at least one division line into a plurality of chipsor dies by the wafer material removal process.

Alternatively, the wafer material may be removed along the at least onedivision line along only part of the thickness of the wafer. Forexample, the wafer material may be removed along 20% or more, 30% ormore, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more,or 90% or more of the thickness of the wafer.

In this case, a process of dividing, i.e., fully dividing, the wafer maybe carried out, for example, by adopting a breaking process, applying anexternal force to the wafer, e.g., using an expansion tape, or byadopting a cutting or dicing process, such as a mechanical cutting ordicing process, a laser cutting or dicing process or a plasma cutting ordicing process. For example, an external force may be applied to thewafer by radially expanding the protective film, i.e., by using theprotective film as an expansion tape. Further, also a combination of twoor more of these processes may be employed.

Moreover, the wafer may be divided by grinding the side of the waferbeing opposite to the one side, as will be further detailed below.

The wafer material may be mechanically removed along the at least onedivision line. In particular, the wafer material may be removed alongthe at least one division line by mechanically cutting the wafer alongthe at least one division line, e.g., by blade dicing or sawing. In thiscase, the wafer is cut from the front side thereof.

Alternatively or in addition, the wafer material may be removed alongthe at least one division line by laser cutting and/or by plasmacutting.

The wafer may be cut in a single mechanical cutting step, a single lasercutting step or a single plasma cutting step. Alternatively, the wafermay be cut by a sequence of mechanical cutting and/or laser cuttingand/or plasma cutting steps.

Laser cutting may be performed, for example, by ablation laser cuttingand/or by stealth laser cutting, i.e., by forming modified regionswithin the wafer by the application of a laser beam, as will be furtherdetailed below, and/or by forming a plurality of hole regions in thewafer by the application of a laser beam. Each of these hole regions maybe composed of a modified region and a space in the modified region opento a surface of the wafer.

By having the protective film attached to the wafer back side, it can beensured that the pressure applied during the cutting step is moreuniformly and homogeneously distributed throughout the wafer duringcutting, thus reducing or even minimising any risk of damage to thewafer, e.g., cracking of the sidewalls of the resulting chips or dies,in the cutting step.

The method may comprise processing the one side of the wafer, whereinprocessing the one side of the wafer comprises or consists of applying apulsed laser beam to the wafer from the one side of the wafer, the waferis made of a material which is transparent to the pulsed laser beam, andthe pulsed laser beam is applied to the wafer at least in a plurality ofpositions along the at least one division line, in a condition where afocal point of the pulsed laser beam is located at a distance from theone side of the wafer in the direction from the one side of the wafertowards the side of the wafer being opposite to the one side, so as toform a plurality of modified regions in the wafer along the at least onedivision line.

In this case, the wafer is made of a material which is transparent tothe pulsed laser beam. Thus, the plurality of modified regions is formedin the wafer by the application of a pulsed laser beam having awavelength that allows transmission of the laser beam through the wafer.For example, if the wafer is a Si wafer, the pulsed laser beam may havea wavelength of 1.0 μm or more.

The pulsed laser beam may have a pulse width, for example, in the rangeof 1 ns to 300 ns.

The modified regions may comprise amorphous regions or regions in whichcracks are formed, or may be amorphous regions or regions in whichcracks are formed. In particularly preferred embodiments, the modifiedregions comprise or are amorphous regions.

Each modified region may comprise a space, e.g., a cavity, inside thewafer material, the space being surrounded by an amorphous region or aregion in which cracks are formed.

Each modified region may be composed of a space, e.g., a cavity, insidethe wafer material and an amorphous region or a region in which cracksare formed surrounding the space.

If the modified regions comprise or are regions in which cracks areformed, i.e., cracks have been formed, the cracks may be microcracks.The cracks may have dimensions, e.g., lengths and/or widths, in the μmrange. For example, the cracks may have widths in the range of 5 μm to100 μm and/or lengths in the range of 100 μm to 1000 μm.

According to this method, the pulsed laser beam is applied to the waferfrom the one side of the wafer at least in a plurality of positionsalong the at least one division line, so as to form a plurality ofmodified regions in the wafer along the at least one division line. Byforming these modified regions, the strength of the wafer in the areasthereof where the modified regions are formed is reduced. Hence,division of the wafer along the at least one division line where theplurality of modified regions has been formed is greatly facilitated. Insuch a wafer division process, the individual devices provided in thedevice area of the wafer are obtained as chips or dies.

The method may further comprise, after forming the plurality of modifiedregions in the wafer, dividing the wafer along the at least one divisionline. The process of dividing the wafer may be carried out in variousways, e.g., by adopting a breaking process, applying an external forceto the wafer, for example, using an expansion tape, or by adopting acutting or dicing process, such as a mechanical cutting or dicingprocess, a laser cutting or dicing process or a plasma cutting or dicingprocess. For example, an external force may be applied to the wafer byradially expanding the protective film, i.e., by using the protectivefilm as an expansion tape. Further, also a combination of two or more ofthese processes may be employed.

The method may comprise processing the side of the wafer being oppositeto the one side. Processing the side of the wafer being opposite to theone side may comprise or consist of applying a pulsed laser beam to thewafer from the side of the wafer being opposite to the one side, whereinthe protective film is made of a material which is transparent to thepulsed laser beam, the wafer is made of a material which is transparentto the pulsed laser beam, and the pulsed laser beam is applied to thewafer at least in a plurality of positions along the at least onedivision line, in a condition where a focal point of the pulsed laserbeam is located at a distance from the side of the wafer being oppositeto the one side in the direction from the side of the wafer beingopposite to the one side towards the one side of the wafer, so as toform a plurality of modified regions in the wafer along the at least onedivision line.

The pulsed laser beam applied from the back side of the wafer may be thesame pulsed laser beam as applied from the front side of the wafer or adifferent pulsed laser beam.

The modified regions formed by applying the pulsed laser beam from theback side of the wafer may be formed substantially in the same manner asthe modified regions formed by applying the pulsed laser beam from thefront side of the wafer.

The protective film may be applied to the side of the wafer beingopposite to the one side so that, in the entire region where the frontsurface of the protective film is in contact with the side of the waferbeing opposite to the one side, the front surface of the protective filmis in direct contact with the side of the wafer being opposite to theone side. Thus, no material, in particular, no adhesive, is presentbetween the front surface of the protective film and the side of thewafer being opposite to the one side.

In this way, the risk of a possible contamination of or damage to thewafer, e.g., due to an adhesive force of an adhesive layer or adhesiveresidues on the wafer, can be reliably eliminated.

Alternatively, the protective film may be provided with an adhesivelayer, wherein the adhesive layer is provided only in a peripheral areaof the front surface of the protective film, the peripheral areasurrounding the central area of the front surface of the protectivefilm, and the protective film is applied to the side of the wafer beingopposite to the one side so that the adhesive layer comes into contactonly with a peripheral portion of the side of the wafer being oppositeto the one side. The peripheral portion of the side of the wafer beingopposite to the one side may correspond to a peripheral marginal areaformed on the one side of the wafer.

In this way, the attachment of the protective film to the wafer can befurther improved. Since the adhesive layer is provided only in theperipheral area of the front surface of the protective film, the area inwhich protective film and wafer are attached to each other by theadhesive layer is significantly reduced as compared to a case where anadhesive layer is provided on the entire front surface of the protectivefilm. Thus, the protective film can be detached from the wafer moreeasily and the risk of damage to the wafer, in particular, toprotrusions formed on the back side thereof, is considerably reduced.

The adhesive of the adhesive layer may be curable by an externalstimulus, such as heat, UV radiation, an electric field and/or achemical agent. In this way, the protective film can be particularlyeasily removed from the wafer after processing. The external stimulusmay be applied to the adhesive so as to lower the adhesive forcethereof, thus allowing for an easy removal of the protective film.

For example, the adhesive layer may have a substantially annular shape,an open rectangular shape or an open square shape, i.e., a rectangularor square shape, respectively, with an opening in the centre of theadhesive layer.

The protective film may be expandable. The protective film may beexpanded when being applied to the side of the wafer being opposite tothe one side. If protrusions are present on the side of the wafer beingopposite to the one side, the protective film may be expanded when beingapplied to the side of the wafer being opposite to the one side so as toclosely or at least partly follow the contours of these protrusions.

In particular, the protective film may be expandable to twice itsoriginal size or more, preferably three times its original size or moreand more preferably four times its original size or more. In this way,in particular, for the case of an expansion to three or four times itsoriginal size or more, it can be reliably ensured that the protectivefilm follows the contours of the protrusions.

If the protective film is expandable it may be used for separating thedevices from each other. In particular, the method may further comprise,after processing the one side of the wafer and/or the side of the waferbeing opposite to the one side, radially expanding the protective filmso as to separate the devices from each other.

For example, the wafer may be fully divided, e.g., by a mechanicalcutting process, a laser cutting process or a plasma cutting process, orby a dicing before grinding process. Subsequently, the fully divideddevices, which may be in the form of chips or dies, may be moved awayfrom each other by radially expanding the protective film, therebyincreasing the distances between adjacent devices.

Alternatively, the wafer may be subjected to a stealth dicing process,i.e., a process in which modified regions are formed within the wafer bythe application of a laser beam, as has been detailed above.Subsequently, the wafer may be divided, e.g., broken, along the at leastone division line where the modified regions are formed by radiallyexpanding the protective film, thereby obtaining individual chips ordies.

As an alternative to radially expanding the protective film, a separateexpansion tape may be attached to the wafer back side, e.g., afterremoving the protective film.

Subsequently, the devices may be separated from each other by radiallyexpanding the expansion tape.

The protective film may be made of a single material, in particular, asingle homogeneous material.

The protective film may be made of a plastic material, such as apolymer. Particularly preferably, the protective film is made of apolyolefin. For example, the protective film may be made of polyethylene(PE), polypropylene (PP) or polybutylene (PB).

Polyolefin films have material properties which are especiallyadvantageous for use in the wafer processing methods of the presentinvention, in particular, if applying the external stimulus to theprotective film comprises or consists of heating the protective film.Polyolefin films are pliable, stretchable and soft when in a heatedstate, e.g., when heated to a temperature in the range of 60° C. to 150°C. Thus, it can be particularly reliably ensured that the protectivefilm conforms to the wafer surface on the side of the wafer beingopposite to the one side, for example, absorbing the wafer topography.This is particularly beneficial if the wafer back side is formed withprotrusions or projections protruding from a plane surface of the wafer.

Further, polyolefin films harden and stiffen upon cooling down, so as tobecome more rigid and robust in the cooled down state. Hence,particularly reliable protection of the wafer during subsequentprocessing of the wafer, such as cutting the wafer, can be ensured.

The protective film may have a thickness in the range of 5 to 200 μm,preferably 8 to 100 μm, more preferably 10 to 80 μm and even morepreferably 12 to 50 μm. Particularly preferably, the protective film hasa thickness in the range of 80 to 150 μm.

In this way, it can be particularly reliably ensured that the protectivefilm is flexible and pliable enough to sufficiently conform to thecontours of protrusions formed on the wafer back side, if suchprotrusions are present, and, at the same time, exhibits a sufficientthickness in order to reliably and efficiently protect the wafer duringprocessing the front side and/or the back side thereof.

A cushioning layer may be attached to a back surface of the protectivefilm opposite to the front surface thereof.

This approach is particularly advantageous, if protrusions orprojections, such as surface unevenness or roughness, bumps, opticalelements, e.g., optical lenses, other structures or the like, protrude,extend or project from the side of the wafer being opposite to the oneside along the thickness direction of the wafer. In this case, theprotrusions or projections define a surface structure or topography ofthe wafer back side, rendering this side uneven.

If the cushioning layer is attached to the back surface of theprotective film, such protrusions can be embedded in the cushioninglayer. Hence, any negative influence of the surface unevenness arisingfrom the presence of the protrusions on subsequent wafer processingsteps, such as cutting, can be eliminated. In particular, the cushioninglayer can significantly contribute to achieving a particularly uniformand homogeneous distribution of pressure during a cutting process.

By embedding the protrusions in the cushioning layer, the protrusions,such as for example optical elements or other structures, are reliablyprotected from any damage during wafer processing, for example, in asubsequent cutting step.

The material of the cushioning layer is not particularly limited. Inparticular, the cushioning layer may be formed of any type of materialwhich allows for protrusions protruding along the thickness direction ofthe wafer to be embedded therein. For example, the cushioning layer maybe formed of a resin, an adhesive, a gel or the like.

The cushioning layer may be curable by an external stimulus, such as UVradiation, heat, an electric field and/or a chemical agent. In thiscase, the cushioning layer hardens at least to some degree uponapplication of the external stimulus thereto. For example, thecushioning layer may be formed of a curable resin, a curable adhesive, acurable gel or the like.

The cushioning layer may be configured so as to exhibit a degree ofcompressibility, elasticity and/or flexibility after curing thereof,i.e., to be compressible, elastic and/or flexible after curing. Forexample, the cushioning layer may be such that it is brought into arubber-like state by curing. Alternatively, the cushioning layer may beconfigured so as to reach a rigid, hard state after curing.

Preferred examples of UV curable resins for use as the cushioning layerin the methods of the invention are ResiFlat by the DISCO Corporationand TEMPLOC by DENKA.

The method may further comprise applying the external stimulus to thecushioning layer so as to cure the cushioning layer, before processing,e.g., cutting, the wafer. In this way, the protection of the waferduring cutting and the cutting accuracy can be further improved.

The cushioning layer may be heat resistant up to a temperature of 180°C. or more, preferably up to a temperature of 220° C. or more, morepreferably up to a temperature of 250° C. or more, and even morepreferably up to a temperature of 300° C. or more.

The cushioning layer may have a thickness in the range of 10 to 300 μm,preferably 20 to 250 μm and more preferably 50 to 200 μm.

The cushioning layer may be attached to the back surface of theprotective film before applying the protective film to the side of thewafer being opposite to the one side.

In this case, the protective film and the cushioning layer may belaminated first, forming a protective sheeting comprising the cushioninglayer and the protective film attached to the cushioning layer. Theprotective sheeting formed in this manner may be subsequently applied tothe side of the wafer being opposite to the one side, e.g., such thatprotrusions or projections protruding from the plane surface of thewafer are covered by the protective film and embedded in the protectivefilm and the cushioning layer. The protective sheeting may be applied sothat the back surface of the cushioning layer is substantially parallelto the one side of the wafer. The front surface of the protective filmis applied to the side of the wafer being opposite to the one side whenthe protective sheeting is applied to the side of the wafer beingopposite to the one side.

In this way, the wafer processing method can be carried out in aparticularly simple and efficient manner. For example, the protectivesheeting can be prepared in advance, stored for later use and used forwafer processing when required. The protective sheeting may thus bemanufactured in large quantities, rendering the production thereofparticularly efficient in terms of both time and cost.

The cushioning layer may be attached to the back surface of theprotective film after applying the protective film to the side of thewafer being opposite to the one side.

In this case, the protective film is applied to the side of the waferbeing opposite to the one side first, and the side of the wafer beingopposite to the one side, having the protective film applied thereto, issubsequently attached to the front surface of the cushioning layer,e.g., so that protrusions or projections protruding from the planesurface of the wafer are embedded in the protective film and thecushioning layer, and the back surface of the cushioning layer issubstantially parallel to the one side of the wafer. This approachallows for the protective film to be attached to the side of the waferbeing opposite to the one side with a particularly high degree ofaccuracy, in particular, in relation to protrusions or projectionsprotruding from the plane surface of the wafer.

The cushioning layer may be attached to the back surface of theprotective film before and/or during and/or after attaching theprotective film to the one side of the wafer.

The method may further comprise removing the protective film and thecushioning layer from the wafer. The protective film and the cushioninglayer may be removed from the wafer after processing, such as cutting,the wafer.

The cushioning layer and the protective film may be removedindividually, i.e., one after the other. For example, the cushioninglayer may be removed first, followed by the removal of the protectivefilm or sheet. Alternatively, the cushioning layer and the protectivefilm may be removed together.

A base sheet may be attached to the back surface of the cushioning layeropposite to the front surface thereof which is attached to theprotective film.

The material of the base sheet is not particularly limited. The basesheet may be made of a soft or pliable material, such as, for example, apolymer material, e.g., polyvinyl chloride (PVC), ethylene vinyl acetate(EVA) or a polyolefin.

Alternatively, the base sheet may be made of a rigid or hard material,such as polyethylene terephthalate (PET) and/or silicon and/or glassand/or stainless steel (SUS).

For example, if the base sheet is made of polyethylene terephthalate(PET) or glass and the cushioning layer is curable by an externalstimulus, the cushioning layer may be cured with radiation that istransmittable through polyethylene terephthalate (PET) or glass, forinstance UV radiation. If the base sheet is made of silicon or stainlesssteel (SUS), a cost-efficient base sheet is provided.

Also, the base sheet may be formed of a combination of the materialslisted above.

The base sheet may be heat resistant up to a temperature of 180° C. ormore, preferably up to a temperature of 220° C. or more, more preferablyup to a temperature of 250° C. or more, and even more preferably up to atemperature of 300° C. or more.

The base sheet may have a thickness in the range of 30 to 1500 μm,preferably 40 to 1200 μm and more preferably 50 to 1000 μm.

The cushioning layer and the base sheet may be attached to the backsurface of the protective film before or after applying the protectivefilm to the back side of the wafer. In particular, the protective film,the cushioning layer and the base sheet may be laminated first, forminga protective sheeting comprising the base sheet, the cushioning layerand the protective film attached to the cushioning layer. The protectivesheeting formed in this manner may be subsequently applied to the waferback side.

The front surface of the base sheet may be in contact with the backsurface of the cushioning layer, and a back surface of the base sheetopposite to the front surface thereof may be substantially parallel tothe one side of the wafer. Thus, when processing, e.g., cutting, the oneside of the wafer, a suitable counter pressure can be applied to theback surface of the base sheet, e.g., by placing this back surface on achuck table.

In this case, since the plane back surface of the base sheet issubstantially parallel to the front side of the wafer, pressure appliedto the wafer during processing, such as a cutting process, e.g., by acutting or dicing blade of a cutting apparatus, is more evenly andhomogeneously distributed over the wafer, thus minimising any risk ofbreakage of the wafer. Further, the substantially parallel alignment ofthe flat, even back surface of the base sheet and the front side of thewafer allows for a cutting step to be carried out with a high degree ofprecision, thus achieving the production of high quality dies or chipswith well-defined shapes and sizes.

The method may further comprise grinding and/or polishing and/oretching, e.g., plasma etching, the side of the wafer being opposite tothe one side, in particular, before applying the protective film to thewafer. The side of the wafer being opposite to the one side may beground for adjusting the wafer thickness.

The invention further provides a method of processing a wafer, having onone side a device area with a plurality of devices, wherein at least onedivision line is formed on the one side of the wafer. The methodcomprises removing wafer material along the at least one division linefrom the one side of the wafer, providing a protective film, and, afterremoving wafer material along the at least one division line, applyingthe protective film, for covering the devices on the wafer, to the oneside of the wafer, so that at least a central area of a front surface ofthe protective film is in direct contact with the one side of the wafer.The method further comprises applying an external stimulus to theprotective film during and/or after applying the protective film to theone side of the wafer, so that the protective film is attached to theone side of the wafer, and, after applying the external stimulus to theprotective film, grinding the side of the wafer being opposite to theone side to adjust the wafer thickness. The wafer material is removedalong only a part of the thickness of the wafer, and grinding the sideof the wafer being opposite to the one side is performed along aremaining part of the thickness of the wafer in which no wafer materialhas been removed, so as to divide the wafer along the at least onedivision line.

The wafer may have the properties, characteristics and featuresdescribed in detail above.

The wafer may have any type of shape. In a top view thereon, the wafermay have, for example, a circular shape, an oval shape, an ellipticalshape or a polygonal shape, such as a rectangular shape or a squareshape.

The protective film may have the properties, characteristics andfeatures described in detail above. In particular, the protective filmmay be used in combination with a cushioning layer or in combinationwith a cushioning layer and a base sheet as described in detail above.

The protective film may have any type of shape. In a top view thereon,the protective film may have, for example, a circular shape, an ovalshape, an elliptical shape or a polygonal shape, such as a rectangularshape or a square shape.

The protective film may have substantially the same shape or the sameshape as the wafer.

The protective film may be applied to the one side of the wafer in thesame manner as detailed above for applying the protective film to theside of the wafer being opposite to the one side.

In particular, the protective film is applied to the one side of thewafer, i.e., to the wafer front side, so that at least the central areaof the front surface of the protective film is in direct contact withthe one side of the wafer. Thus, no material, in particular, noadhesive, is present between at least the central area of the frontsurface of the protective film and the one side of the wafer.

Therefore, the risk of a possible contamination of or damage to thewafer, in particular, the devices formed in the device area, e.g., dueto an adhesive force of an adhesive layer or adhesive residues on thewafer, can be significantly reduced or even eliminated.

The external stimulus and the process of applying the external stimulusto the protective film may have the properties, characteristics andfeatures described in detail above.

In particular, applying the external stimulus to the protective film maycomprise or consist of heating the protective film and/or cooling theprotective film and/or applying a vacuum to the protective film and/orirradiating the protective film with radiation, such as light, e.g., byusing a laser beam.

The external stimulus may comprise or be a chemical compound and/orelectron or plasma irradiation and/or mechanical treatment, such aspressure, friction or ultrasound application, and/or static electricity.

Particularly preferably, applying the external stimulus to theprotective film comprises or consists of heating the protective film.For example, applying the external stimulus to the protective film maycomprise or consist of heating the protective film and applying a vacuumto the protective film. In this case, the vacuum may be applied to theprotective film during and/or before and/or after heating the protectivefilm.

If applying the external stimulus to the protective film comprises orconsists of heating the protective film, the method may further compriseallowing the protective film to cool down after the heating process. Inparticular, the protective film may be allowed to cool down to itsinitial temperature, i.e., to the temperature thereof prior to theheating process. The protective film may be allowed to cool down, e.g.,to its initial temperature, before grinding the side of the wafer beingopposite to the one side, i.e., the wafer back side.

The wafer material may be removed along the at least one division linein the same manner as detailed above.

In particular, the wafer material may be mechanically removed along theat least one division line. For example, the wafer material may beremoved along the at least one division line by mechanically cutting thewafer along the at least one division line, e.g., by blade dicing orsawing.

Alternatively or in addition, the wafer material may be removed alongthe at least one division line by laser cutting and/or by plasmacutting.

The process of removing wafer material along the at least one divisionline may be performed so that, in the plane of the wafer, wafer materialis removed all the way to lateral edges of the wafer, or so that nowafer material is removed in a peripheral portion of the wafer, forexample, in the peripheral marginal area. If no wafer material isremoved in a peripheral portion of the wafer, the device area can beparticularly reliably protected against contamination. In particular,the protective film can be attached to the peripheral portion of thewafer in especially close contact to the wafer surface, thus efficientlysealing the device area.

In the method, grinding of the side of the wafer being opposite to theone side is performed along a remaining part of the thickness of thewafer in which no wafer material has been removed, so as to divide thewafer along the at least one division line. By dividing the wafer in thegrinding step in this way, the wafer can be processed in a particularlyreliable, accurate and efficient manner. Specifically, the step ofremoving wafer material along the at least one division line isperformed on the wafer before grinding, i.e., before a reduction inthickness thereof. Hence, any deformation of the wafer during materialremoval, e.g., during cutting, along the at least one division line,such as wafer warpage or the like, can be reliably avoided. Further, thestress applied to the wafer during wafer material removal along the atleast one division line is significantly reduced, allowing for chips ordies with an increased die strength to be obtained. Any damage to theresulting chips or dies, such as the formation of cracks or back sidechipping, can be prevented.

Moreover, since the wafer material is removed along the at least onedivision line only along part of the wafer thickness, the efficiency, inparticular, the processing speed, of the wafer material removal processis enhanced. Also, the service life of a means, e.g., a cutting means,used for the wafer material removing step is extended.

During and/or after applying the protective film to the one side of thewafer, the external stimulus is applied to the protective film, so thatthe protective film is attached to the one side of the wafer. Anattachment force between protective film and wafer, holding theprotective film in its position on the wafer, is thus generated throughthe application of the external stimulus. Hence, no additional adhesivematerial is necessary for attaching the protective film to the one sideof the wafer. In particular, by applying the external stimulus to theprotective film, a form fit, such as a positive fit, and/or a materialbond, such as an adhesive bond, may be formed between the protectivefilm and the wafer.

The method of the present invention thus enables reliable and efficientprocessing of a wafer having a device area, minimising any risk ofcontamination and damage to the wafer.

The wafer front side surface may be a substantially flat, even surfaceor a flat, even surface.

Alternatively, the device area may be formed with a plurality ofprotrusions or projections protruding from a plane surface of the wafer.The protrusions or projections protruding from the plane surface of thewafer may be embedded in the protective film.

The protrusions or projections, such as bumps, may protrude, extend orproject from a plane surface of the wafer which is a substantially flatsurface. The protrusions or projections may define a surface structureor topography of the one side of the wafer, i.e., the front sidethereof, rendering this one side uneven.

These protrusions or projections may be used, for example, forestablishing an electrical contact with the devices in individual chipsor dies after the wafer has been divided, e.g., when incorporating thechips or dies in electronic equipment, such as mobile phones andpersonal computers.

The protrusions may be irregularly arranged or arranged in a regularpattern. Only some of the protrusions may be arranged in a regularpattern.

The protrusions may have any type of shape. For example, some or all ofthe protrusions may be in the shape of spheres, semi-spheres, pillars orcolumns, e.g., pillars or columns with a circular, elliptic orpolygonal, such as triangular, square etc., cross-section or base area,cones, truncated cones or steps.

At least some of the protrusions may arise from elements formed on theplane surface of the wafer. At least some of the protrusions may arisefrom elements partly or entirely penetrating the wafer in its thicknessdirection, e.g., for the case of a through silicon via (TSV). Theselatter elements may extend along part of the wafer thickness or alongthe entire wafer thickness.

The protrusions may have a height in the thickness direction of thewafer in the range of 20 to 500 μm, preferably 30 to 400 μm, morepreferably 40 to 250 μm, even more preferably 50 to 200 μm and yet evenmore preferably 70 to 150 μm.

All the protrusions may have substantially the same shape and/or size.Alternatively, at least some of the protrusions may differ from eachother in shape and/or size.

In the method of the present invention, the protrusions or projectionsprotruding from the plane surface of the wafer may be embedded in theprotective film. Hence, any negative influence of the surface unevennessarising from the presence of the protrusions in the device area onsubsequent wafer processing steps, in particular, grinding the waferback side, can be reduced or even eliminated.

In particular, by embedding the protrusions in the protective film, theprotrusions can be protected from any damage during wafer processing,for example, in the subsequent grinding step.

Further, if the wafer is ground to a small thickness, e.g., a thicknessin the μm range, the protrusions of the device area on the front side ofthe wafer may cause a deformation of the wafer back side, due to thereduced thickness of the wafer and the pressure applied thereto in thegrinding process. This latter effect is referred to as “patterntransfer”, since the pattern of the protrusions on the wafer front sideis transferred to the wafer back side, and results in an undesiredunevenness of the back side surface of the wafer, thus compromising thequality of the resulting chips or dies.

The protective film acts as a cushion or buffer between the wafer frontside and, for example, a support or carrier on which the wafer frontside rests during processing, e.g., grinding and/or polishing, the waferback side, thus contributing to achieving a uniform and homogeneousdistribution of pressure during processing. Hence, a pattern transfer orbreakage of the wafer during processing, in particular, grinding, theback side thereof can be prevented.

The protective film may be expandable. The protective film may beexpanded when being applied to the one side of the wafer. If protrusionsare present on the one side of the wafer, the protective film may beexpanded when being applied to the one side of the wafer so as toclosely or at least partly follow the contours of these protrusions.

In particular, the protective film may be expandable to twice itsoriginal size or more, preferably three times its original size or moreand more preferably four times its original size or more. In this way,in particular, for the case of an expansion to three or four times itsoriginal size or more, it can be reliably ensured that the protectivefilm follows the contours of the protrusions.

If the protective film is expandable it may be used for separating thedevices from each other. In particular, the method may further comprise,after grinding the side of the wafer being opposite to the one side,radially expanding the protective film so as to separate the devicesfrom each other.

The wafer is fully divided along the at least one division line bygrinding the back side thereof, as has been detailed above.Subsequently, the fully divided devices, which may be in the form ofchips or dies, may be moved away from each other by radially expandingthe protective film, thereby increasing the distances between adjacentdevices. In this way, any damage to the devices due to an unintendedcontact therebetween, e.g., due to adjacent devices touching each otheror rubbing against each other, can be reliably avoided.

The method may comprise, after grinding the side of the wafer beingopposite to the one side, attaching an expandable adhesive tape, such asan expansion tape, to the side of the wafer being opposite to the oneside, and radially expanding the adhesive tape so as to separate thedevices from each other. Also in this way, the fully divided devices maybe moved away from each other, thereby increasing the distances betweenadjacent devices. This approach is particularly advantageous if aprotective film is used which is not expandable.

Prior to attaching the adhesive tape to the side of the wafer beingopposite to the one side, the protective film may be removed.

The method may further comprise, after grinding the side of the waferbeing opposite to the one side, polishing and/or etching, e.g., plasmaetching, the side of the wafer being opposite to the one side.

The protective film may be applied to the one side of the wafer so that,in the entire region where the front surface of the protective film isin contact with the one side of the wafer, the front surface of theprotective film is in direct contact with the one side of the wafer.Thus, no material, in particular, no adhesive, is present between thefront surface of the protective film and the one side of the wafer.

In this way, the risk of a possible contamination of or damage to thewafer, in particular, the devices formed in the device area, e.g., dueto an adhesive force of an adhesive layer or adhesive residues on thewafer, can be reliably eliminated.

Alternatively, the protective film may be provided with an adhesivelayer, wherein the adhesive layer is provided only in a peripheral areaof the front surface of the protective film, the peripheral areasurrounding the central area of the front surface of the protectivefilm, and the protective film is applied to the one side of the wafer sothat the adhesive layer comes into contact only with a peripheralportion of the one side of the wafer, such as the peripheral marginalarea.

In this way, the attachment of the protective film to the wafer can befurther improved. Since the adhesive layer is provided only in theperipheral area of the front surface of the protective film, the area inwhich protective film and wafer are attached to each other by theadhesive layer is significantly reduced as compared to a case where anadhesive layer is provided on the entire front surface of the protectivefilm. Thus, the protective film can be detached from the wafer moreeasily and the risk of damage to the wafer, in particular, toprotrusions formed on the front side thereof, e.g., in the device area,is considerably reduced or even eliminated.

The adhesive of the adhesive layer may be curable by an externalstimulus, such as heat, UV radiation, an electric field and/or achemical agent. In this way, the protective film can be particularlyeasily removed from the wafer after processing. The external stimulusmay be applied to the adhesive so as to lower the adhesive forcethereof, thus allowing for an easy removal of the protective film.

For example, the adhesive layer may have a substantially annular shape,an open rectangular shape or an open square shape.

A cushioning layer may be attached to a back surface of the protectivefilm opposite to the front surface thereof.

The cushioning layer may have the properties, characteristics andfeatures described in detail above. The cushioning layer may be attachedto the back surface of the protective film in the same manner asdetailed above. The disclosure provided above with regard to thecushioning layer fully applies.

Attaching a cushioning layer to the back surface of the protective filmis particularly advantageous if protrusions or projections are presentat the one side of the wafer, in particular, in the device area. In thiscase, the protrusions or projections define a surface structure ortopography of the wafer front side, rendering this side uneven.

If the cushioning layer is attached to the back surface of theprotective film, such protrusions can be embedded in the cushioninglayer. Hence, any negative influence of the surface unevenness arisingfrom the presence of the protrusions on subsequent wafer processingsteps, in particular, grinding the wafer back side, can be eliminated.In particular, the cushioning layer can significantly contribute toachieving a particularly uniform and homogeneous distribution ofpressure during the grinding process. By embedding the protrusions inthe cushioning layer, the protrusions are reliably protected from anydamage during wafer processing, for example, in the grinding step.

The cushioning layer may be attached to the back surface of theprotective film so that the back surface of the cushioning layer issubstantially parallel to the side of the wafer being opposite to theone side.

The cushioning layer may be curable by an external stimulus, such as UVradiation, heat, an electric field and/or a chemical agent.

The method may further comprise applying the external stimulus to thecushioning layer so as to cure the cushioning layer, after applying theprotective film to the one side of the wafer.

A base sheet may be attached to a back surface of the cushioning layer.

The base sheet may have the properties, characteristics and featuresdescribed in detail above. The base sheet may be attached to the backsurface of the cushioning layer in the same manner as detailed above.The disclosure provided above with regard to the base sheet fullyapplies.

A front surface of the base sheet may be in contact with the backsurface of the cushioning layer. A back surface of the base sheetopposite to the front surface thereof may be substantially parallel tothe side of the wafer being opposite to the one side.

In this case, since the plane back surface of the base sheet issubstantially parallel to the back side of the wafer, the pressureapplied to the wafer during processing, such as grinding, e.g., by agrinding wheel of a grinding apparatus, is evenly and homogeneouslydistributed over the wafer, thus minimising any risk of a patterntransfer, i.e., a transfer of a pattern defined by protrusions orprojections in the device area to the processed, in particular, ground,wafer back side, and breakage of the wafer. Further, the substantiallyparallel alignment of the flat, even back surface of the base sheet andthe back side of the wafer allows for the grinding step to be carriedout with a high degree of precision, thus achieving a particularlyuniform and homogeneous wafer thickness after grinding.

Also, the protective film acts as a further cushion or buffer betweenthe wafer front side and the cushioning layer, thus further contributingto the uniform and homogeneous distribution of pressure duringprocessing, such as grinding.

Hence, a pattern transfer or breakage of the wafer during processing canbe particularly reliably prevented.

The invention further provides a method of processing a wafer, having onone side a device area with a plurality of devices. The method comprisesproviding a protective film having an adhesive layer, applying theprotective film, for covering the devices on the wafer, to the one sideof the wafer, so that a central area of a front surface of theprotective film is in direct contact with the one side of the wafer,applying an external stimulus to the protective film during and/or afterapplying the protective film to the one side of the wafer, so that theprotective film is attached to the one side of the wafer, and processingthe side of the wafer being opposite to the one side. The adhesive layeris provided only in a peripheral area of the front surface of theprotective film, wherein the peripheral area surrounds the central areaof the front surface of the protective film. The protective film isapplied to the one side of the wafer so that the adhesive layer comesinto contact only with a peripheral portion of the one side of thewafer, such as a peripheral marginal area of the wafer.

The wafer may have the properties, characteristics and featuresdescribed in detail above.

The wafer may have any type of shape. In a top view thereon, the wafermay have, for example, a circular shape, an oval shape, an ellipticalshape or a polygonal shape, such as a rectangular shape or a squareshape.

The protective film may have the properties, characteristics andfeatures described in detail above. In particular, the protective filmmay be used in combination with a cushioning layer or in combinationwith a cushioning layer and a base sheet as described in detail above.

The protective film may have any type of shape. In a top view thereon,the protective film may have, for example, a circular shape, an ovalshape, an elliptical shape or a polygonal shape, such as a rectangularshape or a square shape.

The protective film may have substantially the same shape or the sameshape as the wafer.

The protective film may be applied to the one side of the wafer in thesame manner as detailed above.

In particular, the protective film is applied to the one side of thewafer, i.e., to the wafer front side, so that the central area of thefront surface of the protective film is in direct contact with the oneside of the wafer. Thus, no material, in particular, no adhesive, ispresent between the central area of the front surface of the protectivefilm and the one side of the wafer.

Therefore, the risk of a possible contamination of or damage to thewafer, in particular, the devices formed in the device area, e.g., dueto the adhesive force of the adhesive layer or adhesive residues on thewafer, can be significantly reduced.

The wafer front side surface may be a substantially flat, even surfaceor a flat, even surface. Alternatively, protrusions or projectionsprotruding from a plane wafer surface along the thickness direction ofthe wafer may be present on the front side of the wafer, in particular,in the device area.

The external stimulus and the process of applying the external stimulusto the protective film may have the properties, characteristics andfeatures described in detail above.

In particular, applying the external stimulus to the protective film maycomprise or consist of heating the protective film and/or cooling theprotective film and/or applying a vacuum to the protective film and/orirradiating the protective film with radiation, such as light, e.g., byusing a laser beam.

The external stimulus may comprise or be a chemical compound and/orelectron or plasma irradiation and/or mechanical treatment, such aspressure, friction or ultrasound application, and/or static electricity.

Particularly preferably, applying the external stimulus to theprotective film comprises or consists of heating the protective film.For example, applying the external stimulus to the protective film maycomprise or consist of heating the protective film and applying a vacuumto the protective film. In this case, the vacuum may be applied to theprotective film during and/or before and/or after heating the protectivefilm.

If applying the external stimulus to the protective film comprises orconsists of heating the protective film, the method may further compriseallowing the protective film to cool down after the heating process. Inparticular, the protective film may be allowed to cool down to itsinitial temperature, i.e., to the temperature thereof prior to theheating process. The protective film may be allowed to cool down, e.g.,to its initial temperature, before processing the side of the waferbeing opposite to the one side, i.e., the wafer back side.

Processing the side of the wafer being opposite to the one side may beperformed in the manner detailed above.

During and/or after applying the protective film to the one side of thewafer, the external stimulus is applied to the protective film, so thatthe protective film is attached to the one side of the wafer. Anattachment force between protective film and wafer, holding theprotective film in its position on the wafer, is thus generated throughthe application of the external stimulus. In particular, by applying theexternal stimulus to the protective film, a form fit, such as a positivefit, and/or a material bond, such as an adhesive bond, may be formedbetween the protective film and the wafer. In addition, the protectivefilm is attached to the wafer by the adhesive layer. In this way, theattachment of the protective film to the wafer is further improved.

Since the adhesive layer is provided only in the peripheral area of thefront surface of the protective film, the area in which protective filmand wafer are attached to each other by the adhesive layer issignificantly reduced as compared to a case where an adhesive layer isprovided on the entire front surface of the protective film. Thus, theprotective film can be detached from the wafer more easily and the riskof damage to the wafer, in particular, to protrusions formed on thefront side thereof, is considerably reduced.

The method of the present invention thus enables reliable and efficientprocessing of a wafer having a device area, minimising any risk ofcontamination and damage to the wafer.

The adhesive of the adhesive layer may be curable by an externalstimulus, such as heat, UV radiation, an electric field and/or achemical agent. In this way, the protective film can be particularlyeasily removed from the wafer after processing. The external stimulusmay be applied to the adhesive so as to lower the adhesive forcethereof, thus allowing for an easy removal of the protective film.

For example, the adhesive layer may have a substantially annular shape,an open rectangular shape or an open square shape.

A cushioning layer may be attached to a back surface of the protectivefilm opposite to the front surface thereof.

The cushioning layer may have the properties, characteristics andfeatures described in detail above. The cushioning layer may be attachedto the back surface of the protective film in the same manner asdetailed above. The disclosure provided above with regard to thecushioning layer fully applies.

Attaching a cushioning layer to the back surface of the protective filmis particularly advantageous if protrusions or projections are presentat the one side of the wafer, in particular, in the device area. In thiscase, the protrusions or projections define a surface structure ortopography of the wafer front side, rendering this side uneven.

If the cushioning layer is attached to the back surface of theprotective film, such protrusions can be embedded in the cushioninglayer. Hence, any negative influence of the surface unevenness arisingfrom the presence of the protrusions on subsequent wafer processingsteps, such as grinding, cutting or polishing, can be eliminated. Inparticular, the cushioning layer can significantly contribute toachieving a particularly uniform and homogeneous distribution ofpressure during such processing. By embedding the protrusions in thecushioning layer, the protrusions are reliably protected from any damageduring wafer processing, for example, in a grinding step.

The cushioning layer may be attached to the back surface of theprotective film so that the back surface of the cushioning layer issubstantially parallel to the side of the wafer being opposite to theone side.

The cushioning layer may be curable by an external stimulus, such as UVradiation, heat, an electric field and/or a chemical agent.

The method may further comprise applying the external stimulus to thecushioning layer so as to cure the cushioning layer, after applying theprotective film to the one side of the wafer.

A base sheet may be attached to a back surface of the cushioning layer.

The base sheet may have the properties, characteristics and featuresdescribed in detail above. The base sheet may be attached to the backsurface of the cushioning layer in the same manner as detailed above.The disclosure provided above with regard to the base sheet fullyapplies.

A front surface of the base sheet may be in contact with the backsurface of the cushioning layer. A back surface of the base sheetopposite to the front surface thereof may be substantially parallel tothe side of the wafer being opposite to the one side.

In this case, since the plane back surface of the base sheet issubstantially parallel to the back side of the wafer, the pressureapplied to the wafer during processing, such as grinding, e.g., by agrinding wheel of a grinding apparatus, is evenly and homogeneouslydistributed over the wafer, thus minimising any risk of a patterntransfer, as has been detailed above. Further, the substantiallyparallel alignment of the flat, even back surface of the base sheet andthe back side of the wafer allows for a grinding step to be carried outwith a high degree of precision, thus achieving a particularly uniformand homogeneous wafer thickness after grinding.

Also, the protective film acts as a further cushion or buffer betweenthe wafer front side and the cushioning layer, thus further contributingto the uniform and homogeneous distribution of pressure duringprocessing, such as grinding. Hence, a pattern transfer or breakage ofthe wafer during processing can be particularly reliably prevented.

Processing the side of the wafer being opposite to the one side maycomprise or consist of grinding the side of the wafer being opposite tothe one side to adjust the wafer thickness.

Processing the side of the wafer being opposite to the one side maycomprise or consist of polishing the side of the wafer being opposite tothe one side, for example, after grinding the side of the wafer beingopposite to the one side.

At least one division line may be formed on the one side of the wafer. Aplurality of division lines may be formed on the one side of the wafer.The one or more division lines partition the devices formed in thedevice area.

Processing the side of the wafer being opposite to the one side maycomprise or consist of removing wafer material along the at least onedivision line, for example, after grinding the side of the wafer beingopposite to the one side. If a plurality of division lines is formed onthe one side of the wafer, processing the side of the wafer beingopposite to the one side may comprise or consist of removing wafermaterial along each of the plurality of division lines, for example,after grinding the side of the wafer being opposite to the one side.

The wafer material may be removed along the at least one division linethroughout the entire thickness of the wafer. In this case, the wafer isdivided along the at least one division line into a plurality of chipsor dies by the wafer material removal process.

Alternatively, the wafer material may be removed along the at least onedivision line along only part of the thickness of the wafer. Forexample, the wafer material may be removed along 20% or more, 30% ormore, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more,or 90% or more of the thickness of the wafer.

In this case, a process of dividing, i.e., fully dividing, the wafer maybe carried out, for example, by adopting a breaking process, applying anexternal force to the wafer, e.g., using an expansion tape, or byadopting a cutting or dicing process, such as a mechanical cutting ordicing process, a laser cutting or dicing process or a plasma cutting ordicing process. For example, an external force may be applied to thewafer by radially expanding the protective film, i.e., by using theprotective film as an expansion tape. Further, also a combination of twoor more of these processes may be employed.

The wafer material may be mechanically removed along the at least onedivision line. In particular, the wafer material may be removed alongthe at least one division line by mechanically cutting the wafer alongthe at least one division line, e.g., by blade dicing or sawing. In thiscase, the wafer is cut from the back side thereof.

Alternatively or in addition, the wafer material may be removed alongthe at least one division line by laser cutting and/or by plasmacutting.

The wafer may be cut in a single mechanical cutting step, a single lasercutting step or a single plasma cutting step. Alternatively, the wafermay be cut by a sequence of mechanical cutting and/or laser cuttingand/or plasma cutting steps.

Laser cutting may be performed, for example, by ablation laser cuttingand/or by stealth laser cutting, i.e., by forming modified regionswithin the wafer by the application of a laser beam, as has beendetailed above, and/or by forming a plurality of hole regions in thewafer by the application of a laser beam. Each of these hole regions maybe composed of a modified region and a space in the modified region opento a surface of the wafer.

In such a stealth laser cutting or stealth dicing process, a pulsedlaser beam may be applied to the wafer from the side of the wafer beingopposite to the one side, wherein the wafer is made of a material whichis transparent to the pulsed laser beam and the pulsed laser beam isapplied to the wafer at least in a plurality of positions along the atleast one division line, in a condition where a focal point of thepulsed laser beam is located at a distance from the side of the waferbeing opposite to the one side in the direction from the side of thewafer being opposite to the one side towards the one side of the wafer,so as to form a plurality of modified regions in the wafer along the atleast one division line.

The method may further comprise, after forming the plurality of modifiedregions in the wafer, dividing the wafer along the at least one divisionline. The process of dividing the wafer may be carried out in variousways, e.g., by adopting a breaking process, applying an external forceto the wafer, for example, using an expansion tape, or by adopting acutting or dicing process, such as a mechanical cutting or dicingprocess, a laser cutting or dicing process or a plasma cutting or dicingprocess. For example, an external force may be applied to the wafer byradially expanding the protective film, i.e., by using the protectivefilm as an expansion tape, as will be further detailed in the following.Further, also a combination of two or more of these processes may beemployed.

The protective film may be expandable. In this case, the protective filmmay be used for separating the devices from each other. In particular,the method may further comprise, after processing the side of the waferbeing opposite to the one side, radially expanding the protective filmso as to separate the devices from each other.

For example, the wafer may be fully divided, e.g., by a mechanicalcutting process, a laser cutting process or a plasma cutting process.Subsequently, the fully divided devices, which may be in the form ofchips or dies, may be moved away from each other by radially expandingthe protective film, thereby increasing the distances between adjacentdevices.

Alternatively, the wafer may be subjected to a stealth laser cutting orstealth dicing process. Subsequently, the wafer may be divided, e.g.,broken, along the at least one division line where the modified regionsare formed by radially expanding the protective film, thereby obtainingindividual chips or dies.

As an alternative to radially expanding the protective film, a separateexpansion tape may be attached to the wafer front side or back side,e.g., after removing the protective film. Subsequently, the devices maybe separated from each other by radially expanding the expansion tape.

The method may comprise, e.g., after grinding the back side of thewafer, attaching an expandable adhesive tape, such as an expansion tape,to the wafer back side. Before or after attaching the adhesive tape tothe wafer back side, the protective film may be removed, so as to exposethe wafer front side.

The method may comprise, e.g., after attaching the adhesive tape to thewafer back side and/or removing the protective film, removing wafermaterial along the at least one division line. The wafer material may beremoved along the at least one division line from the wafer front side.

Removing wafer material along the at least one division line may beperformed in the manner detailed above. For example, the wafer may becut along the at least one division line from the wafer front side, or astealth laser cutting or stealth dicing process may be performed alongthe at least one division line from the wafer front side.

After removing wafer material along the at least one division line orafter performing a stealth laser cutting or stealth dicing process, thedevices may be separated from each other, e.g., by radially expandingthe adhesive tape.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, non-limiting examples of the invention are explained withreference to the drawings, in which:

FIG. 1 is a cross-sectional view showing a wafer to be processed by amethod of the present invention;

FIG. 2 is a perspective view of the wafer shown in FIG. 1;

FIG. 3 is a cross-sectional view showing an embodiment of a protectivesheeting to be used in a method of processing the wafer according to thepresent invention;

FIG. 4 is a cross-sectional view illustrating a step of applying theprotective sheeting shown in FIG. 3 to the wafer shown in FIG. 1 in amethod of processing the wafer according to an embodiment of the presentinvention;

FIG. 5 is a cross-sectional view illustrating a step of applying theprotective sheeting shown in FIG. 3 to the wafer shown in FIG. 1 in amethod of processing the wafer according to another embodiment of thepresent invention;

FIG. 6 is a cross-sectional view showing the outcome of a step ofattaching the protective sheeting to the wafer;

FIG. 7 is a perspective view of the arrangement of the wafer and theprotective sheeting shown in FIG. 6;

FIG. 8 is a cross-sectional view illustrating a cutting step performedon the wafer shown in FIGS. 6 and 7;

FIG. 9 is a cross-sectional view showing the outcome of a step ofattaching a protective film to a wafer in a method of processing thewafer according to another embodiment of the present invention;

FIG. 10 is a cross-sectional view illustrating a cutting step performedon the wafer shown in FIG. 9;

FIG. 11 is a cross-sectional view illustrating a device separating stepperformed after the cutting step shown in FIG. 10;

FIG. 12 is a cross-sectional view illustrating a stealth dicing stepperformed on the wafer shown in FIG. 9;

FIG. 13 is a cross-sectional view showing the outcome of a step ofremoving wafer material in a method of processing the wafer according toanother embodiment of the present invention;

FIG. 14 is a cross-sectional view showing the outcome of a step ofattaching a protective film to the wafer shown in FIG. 13;

FIG. 15A is a top view of the wafer shown in FIG. 13;

FIG. 15B is a top view of the wafer showing the outcome of a modifiedstep of removing wafer material;

FIG. 16 is a cross-sectional view showing the outcome of a step ofgrinding the back side of the wafer shown in FIG. 14;

FIG. 17 is a cross-sectional view showing the outcome of a step ofattaching an adhesive tape to the wafer shown in FIG. 16;

FIG. 18 is a cross-sectional view illustrating a device separating stepperformed after the attachment step shown in FIG. 17;

FIG. 19 is a cross-sectional view showing a wafer to be processed by amethod of the present invention;

FIG. 20 is a cross-sectional view illustrating a step of applying aprotective film to the wafer according to another embodiment of themethod of the present invention;

FIG. 21 is a perspective view illustrating the step of applying theprotective film to the wafer according to the embodiment shown in FIG.20;

FIG. 22 is a cross-sectional view showing the outcome of a step ofattaching the protective film to the wafer;

FIG. 23 is a cross-sectional view showing the outcome of a step ofgrinding the back side of the wafer shown in FIG. 22;

FIG. 24 is a cross-sectional view illustrating a cutting step performedon the wafer shown in FIG. 23;

FIG. 25 is a cross-sectional view illustrating a device separating stepperformed after the cutting step shown in FIG. 24;

FIG. 26 is a cross-sectional view showing the outcome of a step ofattaching an adhesive tape to the wafer shown in FIG. 23; and

FIG. 27 is a cross-sectional view illustrating a cutting step performedon the wafer shown in FIG. 26.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings. The preferred embodimentsrelate to methods for processing a wafer W.

The wafer W can be, for example, a MEMS wafer having MEMS devices formedon the surface of a front side 1 thereof (see FIG. 1). However, thewafer W is not limited to a MEMS wafer, but may also be a CMOS waferhaving CMOS devices, preferably as solid-state imaging devices, formedon the front side 1 thereof or a wafer with other types of devices onthe front side 1.

The wafer W may be made of a semiconductor, e.g., silicon (Si). Such asilicon wafer W can include devices, such as ICs (integrated circuits)and LSIs (large scale integrations), on a silicon substrate.Alternatively, the wafer may be an optical device wafer configured byforming optical devices, such as LEDs (light emitting diodes), on aninorganic material substrate of, for example, ceramic, glass orsapphire. The wafer W is not limited to this and can be formed in anyother way. Furthermore, also a combination of the above describedexemplary wafer designs is possible.

The wafer W can have a thickness before grinding in the μm range,preferably in the range of 625 to 925 μm.

The wafer W preferably exhibits a circular shape. However, the shape ofthe wafer W is not particularly limited. In other embodiments, the waferW may have, for example, an oval shape, an elliptical shape or apolygonal shape, such as a rectangular shape or a square shape.

The wafer W is provided with a plurality of crossing division lines 11(see FIG. 2), also termed streets, formed on the front side 1 thereof,thereby partitioning the wafer W into a plurality of rectangular regionswhere devices 27, such as those described previously, are respectivelyformed. These devices 27 are formed in a device area 2 of the wafer W.In the case of a circular wafer W, this device area 2 is preferablycircular and arranged concentrically with the outer circumference of thewafer W.

The device area 2 is surrounded by an annular peripheral marginal area3, as is schematically shown in FIGS. 1 and 2. In this peripheralmarginal area 3, no devices are formed. The peripheral marginal area 3is preferably arranged concentrically to the device area 2 and/or theouter circumference of the wafer W. The radial extension of theperipheral marginal area 3 can be in the mm range and preferably rangesfrom 1 to 3 mm.

The wafer W further has a back side 6 opposite to the front side 1 (seeFIG. 1). The back side 6 has a plurality of protrusions 14 protrudingalong a thickness direction of the wafer W, as is schematically shown,for example, in FIG. 1. The protrusions 14 may be, for example, surfaceunevenness or roughness, bumps, optical elements, e.g., optical lenses,other structures or the like. The height of the protrusions 14 in thethickness direction of the wafer W may be, for example, in the range of5 to 300 μm. The protrusions 14 illustrated, e.g., in FIG. 1 are notdrawn to scale but shown in enlarged form for better presentability.

In the following, a method of processing a wafer W according to anembodiment of the present invention will be described with reference toFIGS. 1 to 8.

FIG. 1 shows a cross-sectional view of the wafer W to be processed bythe method of the present invention. FIG. 2 shows a perspective view ofthe wafer W shown in cross-section in FIG. 1. FIG. 3 shows across-sectional view of a protective sheeting 5 to be used in the methodof processing the wafer W.

As is shown in FIG. 3, the protective sheeting 5 comprises a base sheet7, a cushioning layer 13 applied to a front surface 17 of the base sheet7, a protective film 4, a back surface of which is attached to thecushioning layer 13, and an adhesive layer 9 applied to a part of afront surface 4 a of the protective film 4 opposite to the back surfacethereof. Specifically, the adhesive layer 9 has an annular shape and isprovided only in a circumferential or peripheral area of the frontsurface 4 a of the protective film 4. The circumferential or peripheralarea surrounds a central area of the front surface 4 a of the protectivefilm 4.

The base sheet 7 and the cushioning layer 13 have a substantiallycircular shape. The outer diameters of the base sheet 7 and thecushioning layer 13 are substantially identical to each other and to theouter diameter of the adhesive layer 9.

The base sheet 7 may, for example, have a thickness in the range of 500to 1000 μm. The protective film 4 may have a thickness in the range of 5to 200 μm. The cushioning layer 13 may have a thickness in the range of10 to 300 μm, preferably 50 to 200 μm.

The cushioning layer 13 is curable by an external stimulus, such as UVradiation, heat, an electric field and/or a chemical agent. Inparticular, the cushioning layer 13 may be formed of a curable resin,such as ResiFlat by DISCO Corporation or TEMPLOC by DENKA.

The protective sheeting 5 is formed by laminating the protective film 4and the base sheet 7 having the cushioning layer 13 applied to the frontsurface 17 thereof.

FIG. 4 illustrates a step of applying the front surface 4 a of theprotective film 4 to the back side 6 of the wafer W.

As is shown in FIG. 4, the annular adhesive layer 9 has an outerdiameter which is larger than the inner diameter of an annular frame 25.Further, the annular adhesive layer 9 has an inner diameter which issmaller than the outer diameter of the wafer W but larger than the outerdiameter of the device area 2. Hence, it can be reliably ensured thatthe adhesive of the adhesive layer 9 comes into contact only with theperipheral portion of the back side 6 of the wafer W, which correspondsto the peripheral marginal area 3 on the front side 1 of the wafer W.

Before applying the protective sheeting 5 to the wafer W, a peripheralportion of the protective sheeting 5 is mounted on the annular frame 25.Further, a back surface 18 of the base sheet 7 opposite to the frontsurface 17 thereof is placed on a chuck table 20. Subsequently, as isindicated by an arrow in FIG. 4, the wafer W is applied to theprotective sheeting 5 placed on the chuck table 20, thereby applying thefront surface 4 a of the protective film 4 to the back side 6 of thewafer W and adhering the protective film 4 to the peripheral portion ofthe back side 6 by the adhesive layer 9. Further, the protrusions 14protruding on the back side 6 of the wafer W are embedded in thecushioning layer 13, as is schematically shown in FIG. 6.

The protective film 4 covers the protrusions 14, thus protecting themagainst damage or contamination. Further, the protective film 4 acts asan additional cushion or buffer in a subsequent cutting step, as will bedetailed below.

The adhesive forming the adhesive layer 9 may be curable by an externalstimulus, such as heat, UV radiation, an electric field and/or achemical agent. In this way, the protective sheeting 5 can beparticularly easily removed from the wafer W after processing.

In particular, the adhesive may be an acrylic resin or an epoxy resin. Apreferred example of a UV curable-type resin for the adhesive is, e.g.,urethane acrylate oligomer.

Further, the adhesive may be, for example, a water soluble resin.

The protective film 4 is made of a polyolefin. For example, theprotective film 4 may be made of polyethylene (PE) or polypropylene(PP).

The protective film 4 is pliable and extendable to approximately threetimes its original diameter.

When applying the wafer W to the protective sheeting 5, the protectivefilm 4 is expanded, e.g., to approximately three times its originaldiameter, so as to closely follow the contours of the protrusions 14, asis schematically shown in FIG. 6.

The back surface 18 of the base sheet 7 is substantially parallel to thefront side 1 of the wafer W, as is indicated by dashed arrows in FIG. 6.

The protective sheeting 5 is applied to the back side 6 of the wafer Wso that the central area of the front surface 4 a of the protective film4, i.e., the area of the front surface 4 a inside the annular adhesivelayer 9, is in direct contact with the back side 6 of the wafer W (seeFIGS. 4 and 6). Thus, no material, in particular, no adhesive, ispresent between the central area of the front surface 4 a of theprotective film 4 and the back side 6 of the wafer W.

After applying the protective sheeting 5 to the back side 6 of the waferW, an external stimulus is applied to the protective film 4 so that theprotective film 4, and thus the protective sheeting 5, is attached,i.e., fully attached, to the back side 6 of the wafer W.

Applying the external stimulus to the protective film 4 may comprise orconsist of heating the protective film 4 and/or cooling the protectivefilm 4 and/or applying a vacuum to the protective film 4 and/orirradiating the protective film 4 with radiation, such as light, e.g.,by using a laser beam.

The external stimulus may comprise or be a chemical compound and/orelectron or plasma irradiation and/or mechanical treatment, such aspressure, friction or ultrasound application, and/or static electricity.

Particularly preferably, applying the external stimulus to theprotective film 4 comprises or consists of heating the protective film4. For example, applying the external stimulus to the protective film 4may comprise or consist of heating the protective film 4 and applying avacuum to the protective film 4. In this case, the vacuum may be appliedto the protective film 4 during and/or before and/or after heating theprotective film 4.

In particular, the protective film 4 may be heated by heating the chucktable 20 (see FIGS. 4 to 6), e.g., to a temperature in the range of 60°C. to 150° C. Particularly preferably, the chuck table 20 is heated to atemperature of approximately 80° C. The chuck table 20 may be heated,for example, over a duration in the range of 1 min to 10 min.

Further, pressure may be applied to the protective sheeting 5 and/or thewafer W so as to press the protective film 4 against the back side 6 ofthe wafer W. For this purpose, a pressure application means (not shown),such as a roller, e.g., a heated roller, may be used. In addition toheating the protective film 4 through the heated chuck table 20, or asan alternative thereto, heat may be applied to the protective film 4 bysuch a heated roller.

By heating the protective film 4, using the heated chuck table 20 and/orthe heated roller, the protective film 4 is attached, i.e., fullyattached, to the back side 6 of the wafer W.

Specifically, an attachment force between the central area of the frontsurface 4 a of the protective film 4 and the back side 6 of the wafer Wis generated through the heating process. In particular, by heating theprotective film 4, a form fit and/or a material bond is formed betweenprotective film 4 and wafer W in this central area.

Further, the peripheral area of the front surface 4 a of the protectivefilm 4 is adhered to the peripheral portion of the back side 6 of thewafer W by the adhesive layer 9, thus ensuring a particularly robust andreliable attachment of the protective sheeting 5.

In the attached state of the protective sheeting 5, which is shown inFIG. 6, the protrusions 14 protruding from the plane back side surfaceof the wafer W are fully embedded in the protective sheeting 5.

By attaching the protective sheeting 5 to the wafer W in the mannerdescribed above, a wafer unit consisting of the wafer W, the protectivefilm 4, the cushioning layer 13 and the base sheet 7 is formed, as isshown in FIGS. 6 and 7.

An alternative approach of attaching the protective sheeting 5 to thewafer W is illustrated in FIG. 5.

Specifically, as is shown in this drawing, the front side 1 of the waferW may be placed on the chuck table 20 so that the back side 6 isoriented upwards. Subsequently, the protective sheeting 5 may be appliedand attached to the back side 6 of the wafer W held on the chuck table20, as is indicated by an arrow in FIG. 5, so that the protrusions 14are embedded in the cushioning layer 13 and the back surface 18 of thebase sheet 7 is substantially parallel to the front side 1 of the waferW. This alternative step of attaching the wafer W and the protectivesheeting 5 to each other can be carried out, for example, in a vacuummounter, such as a vacuum chamber, e.g., the vacuum chamber describedabove.

After attaching the wafer W and the protective sheeting 5 to each other,another external stimulus is applied to the cushioning layer 13 so as tocure the cushioning layer 13. For example, for the case of a heatcurable, e.g., thermosetting, cushioning layer 13, the cushioning layer13 may be cured by heating in an oven. For the case of a UV curablecushioning layer 13, the cushioning layer 13 is cured by the applicationof UV radiation, e.g., through the base sheet 7, if a base sheetmaterial is used which is transparent to this type of radiation, such asPET or glass.

Hence, the protrusions 14 are firmly held in the cured cushioning layer13 and the substantially parallel relative alignment of the base sheetback surface 18 and the pattern side 1 is particularly reliablymaintained throughout the further processing.

It is to be noted, however, that the step of curing the cushioning layer13 described above is optional. Alternatively, the cushioning layer 13may be formed of a non-curable material, such as a non-curable adhesive,a non-curable resin or a non-curable gel, or the cushioning layer 13 maybe formed of a curable material but not be cured in the method ofprocessing the wafer W.

Subsequently, after the optional step of curing the cushioning layer 13,the front side 1 of the wafer W is processed in the state, in which theback surface 18 of the base sheet 7, which is a plane, flat surface, isplaced on the top surface of the chuck table 20 (see FIG. 6). Inparticular, the processing step may comprise or consist of a step ofcutting the front side 1 of the wafer W, e.g., cutting the wafer W alongthe division lines 11. In this way, the wafer W can be divided intoindividual chips or dies, each chip or die having a respective device 27(see FIG. 2).

The step of cutting the wafer W along the division lines 11 is indicatedby dashed lines in FIG. 8. As is illustrated in this drawing, in thepresent embodiment, the wafer W is cut from the front side 1 thereof.The cutting of the wafer W may be performed by mechanical cutting, e.g.,by blade dicing or sawing, and/or by laser cutting and/or by plasmacutting. For example, laser cutting may be carried out by laser ablationor by forming modified layers inside the wafer W along the divisionlines 11 by laser irradiation. The wafer W may be cut in a singlemechanical cutting step, a single laser cutting step or a single plasmacutting step. Alternatively, the wafer W may be cut by a sequence ofmechanical cutting and/or laser cutting and/or plasma cutting steps.Moreover, the cutting process may be carried using a sequence of cuttingsteps with different cutting widths.

Since the plane back surface 18 of the base sheet 7, which is placed onthe top surface of the chuck table 20 that may form part of a cuttingapparatus (not shown), is substantially parallel to the front side 1 ofthe wafer W, the pressure applied to the wafer W, e.g., by a cuttingblade or saw, during the cutting process is evenly and homogenouslydistributed over the wafer W. Hence, any risk of breakage of the wafer Wcan be minimised. Further, the substantially parallel alignment of theflat, even back surface 18 of the base sheet 7 and the front side 1 ofthe wafer W allows for the cutting step to be carried out with a highdegree of precision, thus achieving particularly well-defined anduniform shapes and sizes of the resulting chips or dies.

The protective film 4 covers the protrusions 14 formed on the back side6 of the wafer W, therefore protecting the protrusions 14 from damageand contamination, e.g., by residues of the material forming thecushioning layer 13.

Moreover, the protective film 4 functions as an additional cushion orbuffer between the back side 6 of the wafer W and the cushioning layer13, thus further contributing to the uniform and homogeneousdistribution of pressure during processing, such as cutting. Therefore,breakage of the wafer W during the cutting process can be particularlyreliably prevented.

After the chips or dies have been completely divided from one another inthe cutting step, they may be picked up by a pick-up device (not shown).

Before carrying out this pick-up step, the base sheet 7 and thecushioning layer 13 may be removed from the divided wafer W together, sothat the chips or dies remain on the protective film 4. In this way, theseparated dies or chips can be picked up from the protective film 4 in aparticularly simple and efficient manner. For example, the protectivefilm 4 may be radially expanded, using an expansion drum or the like,thereby increasing a gap between adjacent chips or dies and thusfacilitating the pick-up process. Since the protective film 4 isattached to the back side 6 of the wafer W in the central area and theperipheral area of the front surface 4 a of the protective film 4, bythe application of the external stimulus and by the adhesive layer 9,respectively, this process of separating the chips or dies from eachother can be carried out in a particularly reliable and efficientmanner.

The cushioning layer 13 may exhibit a degree of compressibility,elasticity and/or flexibility, e.g., a rubber-like behavior, aftercuring, thus allowing for a particularly easy removal thereof from thewafer W. Alternatively or additionally, another external stimulus, suchas hot water, may be applied to the cured cushioning layer 13 prior toremoval thereof, in order to soften the cured cushioning layer 13 forfurther facilitating the removal process.

The protective film 4 is arranged on the back side 6 of the wafer W sothat the adhesive of the adhesive layer 9 is in contact only with theperipheral portion of the back side 6, which corresponds to theperipheral marginal area 3 on the front side 1 of the wafer W. Nomaterial, in particular, no adhesive, is present between the centralarea of the front surface 4 a of the protective film 4 and the waferback side 6, i.e., between the protective film 4 and the separated chipsor dies. Hence, the risk of a possible contamination of or damage to thechips or dies, e.g., due to the adhesive force of the adhesive layer 9or adhesive residues on the chips or dies, in the pick-up process iseliminated. In the following, a method of processing a wafer W accordingto another embodiment of the present invention will be described withreference to FIGS. 9 to 12.

The method according to the embodiment of FIGS. 9 to 12 differs from themethod according to the embodiment of FIGS. 1 to 8 mainly in that only aprotective film 4, rather than a protective sheeting 5, is used and inthat no adhesive is provided on the front surface 4 a of the protectivefilm 4 in the entire area where the front surface 4 a and the wafer backside 6 are in contact with each other. Further, no protrusions orprojections are present on the back side 6 of the wafer W. In thedescription of the present embodiment, the elements which are similar orsubstantially identical to those of the embodiment of FIGS. 1 to 8 aredenoted by the same reference signs and a repeated detailed descriptionthereof is omitted.

The device area 2 of the wafer W shown in FIG. 9 is formed with aplurality of protrusions 24 protruding from a plane surface of the waferW. The protrusions 24 may be, for example, bumps for establishing anelectrical contact with the devices of the device area 2 in theseparated chips or dies. The height of the protrusions 24 in thethickness direction of the wafer W may be in the range of 20 to 500 μm.

Before applying the protective film 4 to the wafer W, a peripheralportion of the protective film 4 is mounted on the annular frame 25 (seeFIG. 5). Subsequently, the protective film 4 is applied to the back side6 of the wafer W so that, in the entire region where the front surface 4a of the protective film 4 is in contact with the wafer back side 6, thefront surface 4 a of the protective film 4 is in direct contact with theback side 6. Thus, no material, in particular, no adhesive, is presentbetween the front surface 4 a and the back side 6.

After applying the protective film 4 to the back side 6 of the wafer W,an external stimulus is applied to the protective film 4 so that theprotective film 4 is attached to the back side 6 of the wafer W. Theapplication of the external stimulus to the protective film 4 may beperformed substantially in the same manner as detailed above for theembodiment of FIGS. 1 to 8, in particular, by heating the protectivefilm 4. The outcome of this attachment step is shown in FIG. 9.

Subsequently, the wafer W is processed, i.e., cut along the divisionlines 11 (see FIG. 2), from the front side 1 thereof, as is indicated byarrows and dashed lines in FIG. 10. The cutting step may be performedsubstantially in the same manner as detailed above for the embodiment ofFIGS. 1 to 8.

In this cutting process, the wafer W may be fully divided intoindividual chips or dies, e.g., by a mechanical cutting process, a lasercutting process or a plasma cutting process. Subsequently, the fullydivided chips or dies may be moved away from each other by radiallyexpanding the protective film 4, for example, using an expansion drum orthe like, thereby increasing the distances between adjacent chips ordies, as is shown in FIG. 11. In this way, a following step of pickingup the chips or dies, e.g., by a pick-up device (not shown), issignificantly facilitated.

Moving the chips or dies away from each other by radially expanding theprotective film 4 allows for the chips or dies to be separated in anespecially efficient manner. In particular, no remounting of the waferW, e.g., onto a separate adhesive tape, such as an expansion tape, isnecessary, so that the number of process steps is reduced.

Alternatively, in order to obtain individual chips or dies, the wafer Wmay be subjected to a stealth dicing process, i.e., a process in whichmodified regions are formed within the wafer W by the application of alaser beam, as has been detailed above. The laser beam is applied to thewafer W from the front side 1 thereof. Subsequently, the wafer W may bedivided, e.g., broken, along the division lines 11 where the modifiedregions are formed by radially expanding the protective film 4, as isindicated by two arrows in FIG. 11.

No material, in particular, no adhesive, is present between the frontsurface 4 a of the protective film 4 and the wafer back side 6, i.e.,between the protective film 4 and the separated chips or dies. Hence,the risk of a possible contamination of or damage to the chips or dies,e.g., due to the adhesive force of an adhesive layer or adhesiveresidues on the chips or dies, in the pick-up process is eliminated.

An alternative way of dividing the wafer W is illustrated in FIG. 12. Inthis approach, rather than performing a cutting or stealth dicingprocess from the front side 1 of the wafer W, the wafer W is subjectedto stealth dicing from the back side 6 thereof. In particular, a pulsedlaser beam is applied to the wafer W from its back side 6, as isindicated by arrows in FIG. 12. The protective film 4 is made of amaterial which is transparent to the pulsed laser beam. Hence, the laserbeam is transmitted through the protective film 4 and forms a pluralityof modified regions (indicated by dashed lines in FIG. 12) in the waferW along the division lines 11. After forming these modified regions inthe wafer W, the wafer W may be divided, e.g., broken, along thedivision lines 11 by radially expanding the protective film 4 (see FIG.11).

Performing stealth dicing from the back side 6 of the wafer W isparticularly advantageous if elements, such as metal structures or thelike, are provided on the wafer front side 1 which affect or even blocktransmission of the pulsed laser beam.

In the following, a method of processing a wafer W according to anotherembodiment of the present invention will be described with reference toFIGS. 13 to 18.

In the description of the present embodiment, the elements which aresimilar or substantially identical to those of the previous embodimentsare denoted by the same reference signs and a repeated detaileddescription thereof is omitted. In particular, the wafer W shown in FIG.13 is substantially identical to that shown in FIG. 9.

In the method of this embodiment, wafer material is removed along thedivision lines 11 (see FIGS. 15A and 15B) from the front side 1 of thewafer W. In this process, wafer material is removed along only a part ofthe thickness of the wafer W so as to form grooves 28 extending alongthe division lines 11, as is shown in FIGS. 13, 15A and 15B.

The wafer material may be removed along the division lines 11 in thesame manner as detailed above. In particular, the wafer material may bemechanically removed along the division lines 11. For example, the wafermaterial may be removed along the division lines 11 by mechanicallycutting the wafer W along the division lines 11, e.g., by blade dicingor sawing. Alternatively or in addition, the wafer material may beremoved along the division lines 11 by laser cutting and/or by plasmacutting.

As is shown in FIG. 15A, the process of removing wafer material alongthe division lines 11 may be performed so that the grooves 28 do notextend all the way to lateral edges of the wafer W. In this case, nowafer material is removed in a peripheral portion of the wafer W. Inthis way, the device area 2 can be particularly reliably protectedagainst contamination. In particular, the protective film 4 can beattached to the peripheral portion of the wafer W in especially closecontact to the wafer surface, thus efficiently sealing the device area2.

Alternatively, as is shown in FIG. 15B, the process of removing wafermaterial along the division lines 11 may be performed so that thegrooves 28 extend all the way to the lateral edges of the wafer W.

After removing the wafer material along the division lines 11, theprotective film 4, for covering the devices 27 on the wafer W, isapplied to the front side 1 of the wafer W so that, in the entire regionwhere the front surface 4 a of the protective film 4 is in contact withthe wafer front side 1, the front surface 4 a of the protective film 4is in direct contact with the front side 1. Thus, no material, inparticular, no adhesive, is present between the front surface 4 a of theprotective film 4 and the wafer front side 1. The protective film 4preferably has the same shape as the wafer W, i.e., a circular shape inthe present embodiment, and is concentrically attached thereto. Thediameter of the protective film 4 is approximately the same as that ofthe wafer W, as is schematically shown in FIG. 14.

After applying the protective film 4 to the front side 1 of the wafer W,an external stimulus is applied to the protective film 4 so that theprotective film 4 is attached to the front side 1. The application ofthe external stimulus to the protective film 4 may be performedsubstantially in the same manner as detailed above for the embodiment ofFIGS. 1 to 8, in particular, by heating the protective film 4. Theoutcome of this attachment step is shown in FIG. 14. In the attachedstate of the protective film 4, the protrusions 24 protruding from theplane surface of the wafer front side 1 are fully embedded in theprotective film 4.

Subsequently, the back side 6 of the wafer W is ground to adjust thewafer thickness. Grinding the wafer back side 6 is performed along aremaining part of the thickness of the wafer W in which no wafermaterial has been removed, so as to divide the wafer W along thedivision lines 11, thereby obtaining individual chips or dies. Theoutcome of this grinding step is shown in FIG. 16. After grinding theback side 6 of the wafer W, the back side 6 may be polished and/oretched, e.g., plasma etched.

In a following step, an expandable adhesive tape 30, such as anexpansion tape, is attached to the ground back side 6 of the wafer W. Aperipheral portion of the adhesive tape 30 is mounted on an annularframe 25. The outcome of this attachment step is shown in FIG. 17.

After the adhesive tape 30 has been attached to the ground wafer backside 6, the protective film 4 is removed. The adhesive tape 30 is thenradially expanded, e.g., by using an expansion drum or the like, as isindicated by two arrows in FIG. 18, so as to move the divided chips ordies away from each other, thereby increasing the distances betweenadjacent chips or dies. Subsequently, the chips or dies may be pickedup, e.g., by using a pick-up device (not shown).

In the following, a method of processing a wafer W according to anotherembodiment of the present invention will be described with reference toFIGS. 19 to 27.

In the description of the present embodiment, the elements which aresimilar or substantially identical to those of the previous embodimentsare denoted by the same reference signs and a repeated detaileddescription thereof is omitted. In particular, the wafer W shown in FIG.19 is substantially identical to that shown in FIG. 9.

In the method of this embodiment, a protective film 4 having an adhesivelayer 9 is applied, for covering the devices 27 on the wafer W, to thefront side 1 of the wafer W (as is indicated by an arrow in FIG. 20), sothat a central area of the front surface 4 a of the protective film 4 isin direct contact with the front side 1 of the wafer W. Thus, nomaterial, in particular, no adhesive, is present between the centralarea of the front surface 4 a of the protective film 4 and the waferfront side 1.

The adhesive layer 9 has an annular shape and is provided only in aperipheral area of the front surface 4 a of the protective film 4. Theperipheral area surrounds the central area of the front surface 4 a ofthe protective film 4. The protective film 4 is applied to the waferfront side 1 so that the adhesive of the adhesive layer 9 comes intocontact only with a peripheral portion of the front side 1. Thisperipheral portion of the front side 1 is arranged within the peripheralmarginal area 3 in which no devices 27 are formed. In this regard, it isto be noted that the adhesive layer 9 is not shown in FIGS. 22 to 24 forthe sake of simpler presentation.

The protective film 4 preferably has the same shape as the wafer W,i.e., a circular shape in the present embodiment, and is concentricallyattached thereto. The diameter of the protective film 4 is approximatelythe same as that of the wafer W, as is schematically shown in FIGS. 21and 22.

The protective film 4 covers the devices 27 formed in the device area 2,including the protrusions 24, thus protecting the devices 27 againstdamage or contamination. Further, the protective film 4 acts as acushion in subsequent processing of the wafer W, e.g., in a subsequentgrinding step.

After applying the protective film 4 to the front side 1 of the wafer W,an external stimulus is applied to the protective film 4 so that theprotective film 4 is attached, i.e., fully attached, to the wafer frontside 1. The application of the external stimulus to the protective film4 may be performed substantially in the same manner as detailed abovefor the embodiment of FIGS. 1 to 8, in particular, by heating theprotective film 4. The outcome of this attachment step is shown in FIG.22. In the attached state of the protective film 4, the protrusions 24protruding from the plane surface of the wafer front side 1 are fullyembedded in the protective film 4.

An attachment force between the central area of the front surface 4 a ofthe protective film 4 and the front side 1 of the wafer W is generatedthrough the application of the external stimulus, e.g., the heatingprocess. In particular, by heating the protective film 4, a form fitand/or a material bond may be formed between protective film 4 and waferW in this central area.

Further, the peripheral area of the front surface 4 a of the protectivefilm 4 is adhered to the peripheral portion of the front side 1 of thewafer W by the adhesive layer 9, thus ensuring a particularly robust andreliable attachment of the protective film 4.

After attaching the protective film 4 to the front side 1 of the waferW, the back side 6 of the wafer W is processed. The back side 6 of thewafer W may be processed by grinding and/or polishing and/or etchingand/or cutting.

In the method of the present embodiment, the wafer back side 6 is groundto adjust the wafer thickness after attaching the protective film 4 tothe wafer front side 1. The outcome of this grinding step is shown inFIG. 23. After grinding the back side 6 of the wafer W, the back side 6may be polished and/or etched, e.g., plasma etched.

Subsequently, the ground wafer back side 6 is further processed, i.e.,cut along the division lines 11 (see FIG. 21), as is indicated by arrowsand dashed lines in FIG. 24. The cutting step may be performedsubstantially in the same manner as detailed above for the embodiment ofFIGS. 1 to 8.

In this cutting process, the wafer W may be fully divided intoindividual chips or dies, e.g., by a mechanical cutting process, a lasercutting process or a plasma cutting process. Subsequently, an expandableadhesive tape 30, such as an expansion tape, may be attached to theground back side 6 of the wafer W (see FIG. 25).

After the adhesive tape 30 has been attached to the ground wafer backside 6, the protective film 4 may be removed. The adhesive tape 30 maythen be radially expanded, e.g., by using an expansion drum or the like,as is indicated by two arrows in FIG. 25, so as to move the dividedchips or dies away from each other, thereby increasing the distancesbetween adjacent chips or dies. Subsequently, the chips or dies may bepicked up, e.g., by using a pick-up device (not shown).

Alternatively, in order to obtain individual chips or dies, the wafer Wmay be subjected to a stealth dicing process from the ground back side 6thereof. Subsequently, the adhesive tape 30 may be attached to theground back side 6 of the wafer W, the protective film 4 may be removed,and the wafer W may be divided, e.g., broken, along the division lines11 where the modified regions are formed by radially expanding theadhesive tape 30 (see FIG. 25).

An alternative way of dividing the wafer W is illustrated in FIGS. 26and 27. In this approach, after grinding the back side 6 of the wafer W,the adhesive tape 30 is attached to the ground wafer back side 6 and theprotective film 4 is removed. The peripheral portion of the adhesivetape 30 is mounted to the annular frame 25. The outcome of theseattachment and removal steps is shown in FIG. 26.

Subsequently, the wafer W is subjected to cutting or stealth dicingalong the division lines 11 from the front side 1 thereof, as isindicated by arrows and dashed lines in FIG. 27.

1. A method of processing a wafer, having on one side a device area witha plurality of devices, wherein at least one division line is formed onthe one side of the wafer, and the method comprises: removing wafermaterial along the at least one division line from the one side of thewafer; providing a protective film; after removing wafer material alongthe at least one division line, applying the protective film, forcovering the devices on the wafer, to the one side of the wafer, so thatat least a central area of a front surface of the protective film is indirect contact with the one side of the wafer such that no adhesive ispresent between at least the central area of the front surface of theprotective film and the one side of the wafer, and no adhesive is indirect contact with at least a central area of a surface of the one sideof the wafer; applying an external stimulus to the protective filmduring and/or after applying the protective film to the one side of thewafer, so that the protective film is attached to the one side of thewafer; and after applying the external stimulus to the protective film,grinding the side of the wafer being opposite to the one side to adjustthe wafer thickness, wherein the wafer material is removed along only apart of the thickness of the wafer, and grinding the side of the waferbeing opposite to the one side is performed along a remaining part ofthe thickness of the wafer in which no wafer material has been removed,so as to divide the wafer along the at least one division line.
 2. Themethod according to claim 1, wherein the protective film is expandable,and the method further comprises, after grinding the side of the waferbeing opposite to the one side, radially expanding the protective filmso as to separate the devices from each other.
 3. The method accordingto claim 1, further comprising, after grinding the side of the waferbeing opposite to the one side: attaching an adhesive tape to the sideof the wafer being opposite to the one side, and radially expanding theadhesive tape so as to separate the devices from each other.
 4. Themethod according to claim 3, further comprising, after grinding the sideof the wafer being opposite to the one side, polishing the side of thewafer being opposite to the one side.
 5. The method according to claim4, wherein the protective film is provided with an adhesive layer, theadhesive layer is provided only in a peripheral area of the frontsurface of the protective film, the peripheral area surrounding thecentral area of the front surface of the protective film, and theprotective film is applied to the one side of the wafer so that theadhesive layer comes into contact only with a peripheral portion of theone side of the wafer.
 6. The method according to claim 5, wherein acushioning layer is attached to a back surface of the protective filmopposite to the front surface thereof.
 7. The method according to claim6, wherein a base sheet is attached to a back surface of the cushioninglayer.
 8. The method according to claim 7, wherein a front surface ofthe base sheet is in contact with the back surface of the cushioninglayer, and a back surface of the base sheet opposite to the frontsurface thereof is substantially parallel to the side of the wafer beingopposite to the one side.
 9. The method according to claim 8, whereinthe cushioning layer is curable by an external stimulus, such as UVradiation, heat, an electric field and/or a chemical agent.
 10. Themethod according to claim 9, further comprising applying the externalstimulus to the cushioning layer so as to cure the cushioning layer,after applying the protective film to the one side of the wafer.
 11. Amethod of processing a wafer, having on one side a device area with aplurality of devices, wherein the method comprises: providing aprotective film having an adhesive layer; applying the protective film,for covering the devices on the wafer, to the one side of the wafer, sothat a central area of a front surface of the protective film is indirect contact with the one side of the wafer such that no adhesive ispresent between the central area of the front surface of the protectivefilm and the one side of the wafer, and no adhesive is in direct contactwith a central area of a surface of the one side of the wafer; applyingan external stimulus to the protective film during and/or after applyingthe protective film to the one side of the wafer, so that the protectivefilm is attached to the one side of the wafer; and processing the sideof the wafer being opposite to the one side, wherein the adhesive layeris provided only in a peripheral area of the front surface of theprotective film, the peripheral area surrounding the central area of thefront surface of the protective film, and the protective film is appliedto the one side of the wafer so that the adhesive layer comes intocontact only with a peripheral portion of the one side of the wafer. 12.The method according to claim 11, wherein processing the side of thewafer being opposite to the one side comprises grinding the side of thewafer being opposite to the one side to adjust the wafer thickness. 13.The method according to claim 11, wherein applying the external stimulusto the protective film comprises heating the protective film and/orcooling the protective film and/or applying a vacuum to the protectivefilm and/or irradiating the protective film with light.
 14. The methodaccording to claim 1, wherein applying the external stimulus to theprotective film comprises heating the protective film and/or cooling theprotective film and/or applying a vacuum to the protective film and/orirradiating the protective film with light.
 15. The method according toclaim 1, wherein the protective film is made of a polymer, inparticular, a polyolefin.
 16. The method according to claim 11, whereinthe protective film is made of a polymer, in particular, a polyolefin.